Unbelievers often argue that Christianity cannot be true because there are too many denominations. In reality, a large number of denominations is exactly what we would expect if the Bible is true. This is because the Bible itself is littered with warnings that false religions would appear, and in fact already were appearing, that not only worshiped false gods, but would even claim allegiance to the real God, to Christ Himself, and to the Gospel.
The official position of this ministry is that there are true Christians in every denomination, but there are no Christian denominations. The Bible specifically warns against denominations by pointing out that Christ is not divided (1 Corinthians 1:13). There's only one Christ, He's never going to change (Hebrews 13:8) and the faith He gave us was delivered once for all (Jude 1:3). Point being, Christianity should be the same for everyone.
And yet, judging by the aforementioned number of denominations, it's apparently not. Why? Especially if I'm going to claim there are true Christians in all of them. For this, we first need to ask what is a Christian? The term "Christian" was first used to describe the disciples in Antioch (Acts 11:26). If the disciples were called Christians (and God sees fit to use this term later for the faith, as He does in 1 Peter 4:16), then Christianity must be the faith of the disciples. We also see Agrippa claiming Paul had almost convinced him to become a Christian (Acts 26:28), to which Paul effectively replied "I wish you would, and everyone here, too."
This gives us a standard. Christianity is the religion the disciples preached. But as we dig deeper into the Scriptures, we find that even the Apostles did not believe themselves to be the highest authority. Paul, for example, stated "But even if we, or an angel from heaven, preach any other gospel to you than what we have preached to you, let him be accursed." (Galatians 1:8, emphasis mine). In 2 Peter 1:20-21, Peter reinforced his claim that he and his fellow Christians were not following "cunningly devised fables" (verse 16) by claiming that no prophecy of Scripture is of any private interpretation, but that the prophets wrote as they were guided by the Holy Spirit. The religion the disciples preached was considered to be very much above themselves, coming directly from the God they followed. More specifically, the Gospel they preached centred around God in flesh, the man Jesus Christ, from whom the term Christ-ianity is derived.
So, Christianity is the religion that the disciples preached, but it is, more importantly, a religion that was preached to them. They weren't acting on their own authority, but on the authority of the Holy Spirit, who spoke by the authority of Christ (John 16:13) who spoke by the authority of the Father (John 14:10). Because the disciples did not speak on their own authority, even they were capable of making mistakes. Peter, for example, made a rather large mistake in trying to compel the Gentile Christians to behave as Jews, and he even lead Barnabas astray in this regard (Galatians 2:11-21).
So we see that even the disciples, most of whom had walked with Jesus during His ministry (Paul being the exception, and ironically the one who corrected Peter in this case), all of whom were guided by the Holy Spirit, and none of whom would have had any motive to intentionally spread a lie, were still capable of making mistakes. Scale this up a bit and we understand that even a congregation of true believers can fall like dominoes if an authority figure (as Peter was to Barnabas) makes such a mistake. What's more is that while Paul corrected Peter, there is very rarely a Pauline figure to correct those leaders whose faith is true, yet still make these mistakes.
But mistakes are not always accidental. Satan's favorite and most effective strategy is to erect false churches, a strategy which sinful human beings are all too happy to support him in. There are a number of benefits to starting a false church, or to infiltrating an existing church to lead it astray. Money, power, fame, and even a front for more sinister works, are all things that are strongly desired by our feeble species, and if you play your cards right, starting a false church will lead to such things. The result is a number of pseudo-Christian religions, which are called "denominations", popping up from the first century all the way up to today's world.
The Bible details a number of doctrines. Some of these doctrines are essential (i.e. dissent is an automatic disqualification as a Christian), some are important (i.e. dissent is ill advised and sinful, but will not necessarily lead to Hell), some are disputable (i.e. the Bible gives us everything we need to know about it, but we might disagree, and that's ok) and some just don't matter (i.e. a Christian has options, the Scriptures don't give a universally applicable judgement).
An example of the latter category is dietary laws. The New Testament is clear that there aren't any. Yet, some Christians may choose to be vegetarians. No one is allowed to tell a Christian he can't be a vegetarian, neither are vegetarian Christians allowed to judge those who eat meat. See, for example, Romans 14.
An example of a disputable doctrine is eschatology. Just as Old Testament prophecies were hard to understand until they started coming to pass, so also are end time prophecies difficult to understand now. The Church has a range of opinions about end time prophecy (some of which depends on denominations), but ultimately, it's not supposed to matter. You can be a Christian and believe the rapture will occur before the tribulation, you can be a Christian and believe the rapture will occur after the tribulation. There are Biblical merits to both views, and unless the Holy Spirit decides He wants you in particular to understand them, you're not likely to be 100% correct about it. In all likelihood, it won't affect you anyway. The Church has been awaiting the Lord's return for nearly 2,000 years, and may well need to for another 2,000.
An example of an important doctrine is the doctrine of Creation. The doctrine of Creation can neither save, nor can it condemn, but its clarity ultimately means that it is a matter of believing or rejecting the word of God. Furthermore, the doctrine of Creation is a foundation for a number of other doctrines, so an erroneous view of it will lead to an erroneous view of those.
An example of an essential doctrine is the Trinity. The triune nature of God is extremely confusing. The Bible repeatedly affirms that there is only one God, yet repeatedly affirms three individual beings as God. As confusing as it is, one cannot be saved without believing this doctrine, because its denial requires rejecting Jesus as Lord, yet one cannot be saved without accepting Him as Lord.
Putting all of this together, we see that a plethora of denominations are certainly not an argument against Christianity. The majority of denominations are not even mutually exclusive, the differences between them being minor. Very few disputes arise between these, to the point where if someone identifies as a Christian, other Christians will rarely have to tread the same eggshells with them as they would with a non-Christian. Denominations that do have major differences often do so because of the mis-categorisation of a "lower" (i.e. non-essential) doctrine. Other denominations, and I dare say the best examples happen to be the ones with the biggest spotlight on them, are blatantly unChristian due to their conflict with an essential or important doctrine.
Regardless of how Christian or not a denomination is, the fact remains that a Christian need neither be loyal to any, nor will they lose their salvation for claiming allegiance to any of them. Individual denominations are far too complex for anyone to fully grasp anyway, which ultimately means that one can follow a denomination in name only, in much the same way one can follow Christianity in name only. All of this ultimately means that to argue against Christianity because of the number of denominations is futile. Christianity expects a number of denominations to arise, for a number of reasons. The real argument against it would be if there was only one denomination. Unfortunately, the Church will never be so united as to make such an argument a possibility.