Vicously attack. Wrong? Hmm, I don't know for sure. I do not think it is a good way to attract others to Christianity. No one is attracted to judgement, hatred, and non-constructive criticism. Instead, try simply stating why it is you who is right, and they who are wrong. Do not yell. Do not snarl. This is unpleasent. If you wish to steer away those that might be mildly interested, this is the best way. It worked on me for quite some time. Those that have no interest, and speak against it. Hellfire and ****ation, may be the rheteroic they need, but not the only rhetoric.
I could be wrong, maybe I'm a little bit more compassionate on this issue because of experience. Many Christians are very hateful toward those that are not like them. I have many foriegn friends. I have a very devout muslim friend in Damascus, he tried to convert me. I told him, that even if I did believe that Islam was correct, that would be cultural suicide in America. I have a bhuddist friend in Sri Lanka, she is very kind and considerate. Atleast I think she is bhuddist. She keeps sending emails about god though. I could be wrong.
I can think of one reason why attacking a religion that isn't christian or jewish could be justifiable, it happens in the old testament a few times. I think. I'm not certain. Then again, what about the Crusades? Where did that get Christianity in the middle east? One could argue that it greatly weakened Christianity in the middle east. Then again, it could of strengthened it in the long run.
I voted no, but I admit, that I may not be solely correct. I just know from experience, expressing judgement, hatred, and many other related emotions to a non-christian, that might be slightly interested, is a good way to deter that interest. Happens to me still. So much hatred comes from the "social groups" who go to church where I live, just because they are the locals and that's what their parents did. They then speak down to anyone who isn't part of that circle.