Imagine, if you are Muslim, how you might feel if someone comes to you telling you about your own religion. Imagine someone who isn't Muslim telling you that Islam teaches this, preaches that, and you believe thus-and-such, and that this person is actually wrong. Because you don't believe whatever it is he's saying you do believe.
In fact this happens quite a lot--many people like to get up and say what Muslims believe. Usually it's in the context of trying to blame Islam for terrorism (or even to use Islam for terrorism.) It's popular to hear people who aren't Muslim saying "Muslims believe that..." and launching into an absurd rant about killing infidels or something equally ludicrous. Because this happens, as Muslims we should be easily able to understand the sentiment I am about to describe.
Imagine now a non-Muslim being told about his beliefs by a Muslim. In other words, the Muslim is telling that non-Muslim that he believes something in particular--and the Muslim might even cite the Qur'an--but that non-Muslim actually doesn't believe it. For example, I've yet to come across any Jews anywhere who say that Uzair (I guess in English it is Ezra?) is the son of God. And I don't mean to dispute the Qur'an on the issue at all--though it certainly doesn't say that all Jews espouse such a belief. And without bothering to really listen to our Jewish neighbors about their beliefs in the first place, it's kind of arrogant, I think, to try to prove what they believe when we are in fact the ones in error. It does nothing to strengthen the position of Islam or Muslims, or to further the da'wah.
I can't imagine it to be anything but rude or offensive to tell a person what he believes. Now that is just my opinion, but does anyone have reason to believe that such bullying da'wah techniques could ever be effective?