It used to be a well recognised fact that the only people who had a problem with the concept of truth were liars. Those who believed the truth were not offended by truth because they believed it. Those who believed falsehoods were not offended by truth because, while wrong, they at least believed they were right. Even liars spread their lies by presenting them as the truth.
In our modern world, however, it has almost become noble to reject the truth. No matter how firmly one believes a given statement, one is encouraged to acknowledge that alternatives, no matter how unreasonable, are valid. To express your beliefs as true is seen as "intolerant" and "bigoted". Unless, of course, your beliefs are Relativism and/or Agnosticism. This worldview is both dishonest and self refuting, as is shown by the simple question seen in the header image: Is Christianity true, or not?
There are a grand total of three answers to this question: Yes, no, and I don't know. In all three cases, it is impossible to honestly tell a Christian they should not preach it.
If you answer "yes", then telling Christians not to preach it is both intolerant and dishonest. It is intolerant because it denies a man the right to preach the truth, while simultaneously preaching a lie. If you believe a Christian has no right to preach the truth, you are very intolerant if you think you have the right to tell him what you believe. But it's dishonest because you don't even believe it! You know Christianity is true, and yet you act as if it is not, and demand others do so too.
If your answer is "no", then by your own standards, you are intolerant. If Christianity is not true, Christians at least believe it is true, and so are acting in good faith when they preach it. If you think they're wrong, challenge them, but find better arguments than "you're intolerant", because you, yourself, are intolerant by your own definition! If it's intolerant to preach "I'm right" or "you're wrong", you cannot tell a Christian "I'm right because you're intolerant", or "you're wrong because you're intolerant".
The answer "I don't know" takes on the flaws of both answers: You teach people to act as if Christianity is not true while simultaneously not knowing that it isn't. In other words, you're intolerant towards Christians by your own standards, and yet you may also be actively encouraging them to lie.
The mere claim that your beliefs are true is not intolerant. In fact, I will say outright that I have far greater respect for someone who disagrees with me firmly than someone who "tolerates" my views for the sake of appearing tolerant. If you do not have the spine to stand for what you believe in, you can flop right on out of the discussion, because no sane person wants to play a game where the only rule is "don't win".
The truth is, it is entirely possible to tolerate, and even love those with whom you disagree. Jesus, the God of Christianity, proved this when He died for our sins while we were still in them. See, God is very intolerant, and justifiably so. What fellowship does light have with darkness? Do you tolerate a man who breaks into your house to steal your property and hurt your family? Why, then, should a Holy God tolerate unholy people? And yet, He does not tolerate us, He loves us, and so He died to make us clean. And so you should not only tolerate when Christians, in love and good faith, preach to you. You should hear them out. They carry the message of eternal life to you. Hear it. Receive it. Confess Jesus as Lord, believing He rose from the dead, and you will be saved.