There are two ways the world tries to suppress Christian preaching. The first is rather obvious, and pathetically uncreative: "Shut your mouth, or we'll shut it for you". Mindless aggression, and even violence, are very easy for impenitent sinners to engage in. The second way is far more crafty, even if the sinner in question does not realise how sneaky they are being. That is to give silence the appearance of wisdom, or even compassion.
Whatever your religious orientation, we all know that we are not omniscient. It is entirely possible that we are wrong about everything we think we know, including Christianity. Another thing we all know is that we all live in this world together. Thus, for sake of peace, we should all tolerate each other, regardless of our beliefs, and we should never seek to change each other's beliefs.
This approach has a far greater emotional appeal. When we endure violence for our faiths, we at least feel justified in knowing that our opponents have to resort to such folly. But the Agnostic approach of "we can't know the truth, so let's just try to get along" makes you seem like the hot-headed bad guy if you continue in your "intolerant" habits of preaching your religion.
Let us first deal with the hypocrisy of this. When you tell someone "we should not preach our beliefs", are you not preaching your beliefs? When you tell someone "we should not try to change each other's beliefs", are you not trying to change their beliefs? Heck, when you tell someone "we can't know the truth", you are technically saying "I know Christianity is not true", for Christ Himself declares "ye shall know the truth, and the truth shall make you free" (John 8:32). In other words, preaching any of these Agnostic philosophies is self refuting. If you really believe we shouldn't preach our beliefs, you should shut up, unless, of course, you're claiming your beliefs are superior. No matter which way you cut the cake, you have no high ground to stand upon, either morally, or intellectually.
But this gets worse when we ask you the question "if Christianity is true, would you want to know it?" If you answer "yes", then there is no inconsistency in Christians preaching. See, we believe it is true, and so regardless of whether you think we are right, or even regardless of whether we are right, we are simply acting in the way you literally just said you would want us to. So there are two possibilities here. The first is that we absolutely should be preaching Christianity, even to you.
But the second possibility is that you were lying when you said you would want to know if Christianity is true. Whether this is merely implicit, or if you gave this answer in the first place, your problem isn't that it is ignorant or intolerant to preach Christianity, but that you are willfully ignorant, and intolerant, for not only do you not care about truth, but you selfishly impose that willful ignorance upon others.
In the case of the former, it is beneficial to you that we preach, not just because we think we are right, but because we are right. We, as Christians, believe in a God who entered creation as a man, died on a cross, and then rose from the dead. He warns us that we have all sinned against God, and have earned eternal punishment, but He also gives us a message of reconciliation to God, by which our faith is rewarded instead. In the case of the latter, preaching to you is worthless simply because you will not accept it, but because of your self deceit, no one needs it more than you. You're like a man who would rather bleed out than let us call you an ambulance. You would rather burn than follow a firefighter to safety. Rather than lawyer up, you revel in your crimes, laughing as the judge brings down his gavel. Such folly, but not on the part of the preacher. It is on you.
Regardless of whether you believe Christianity is true, and even regardless of whether it is true, there is no scenario in which a Christian is morally or intellectually wrong to preach. The moral and intellectual errors are on the part of those who claim not to know truth, but seek to discourage those who believe they have found it from sharing it. Therefore, Agnosticism is a symptom of a dishonest heart, and those who hold to it, and especially those who preach it, should immediately repent, and turn in faith to the God who forgives sins far greater than their own.