You might find that if you talk face to face with an individual with whom you share religious differences, it would be a really civil conversation. It's these online forums that breed all the nastiness. It's made ever worse by the way people tend to read a post by someone disagreeing with them, and assume the tone is belligerent.
What I've noticed is that it's not so much a relentless attack on each other's religions as it is a hate response to those who believe in Christ. There are several denominational views expressed and it seems that mainly communication without an onslaught of rude and hateful remarks come. But, when a person asks a question and it is evident that the asker comes from a viewpoint of Christian belief, instead of approaching their question in a sincere effort to answer, there is oftentimes, an outright attack to that person being a believer of Jesus.
I've experienced that not all are like that. Actually, the most educated ones are not like it. The less educated, the more they seem to verbally attack. They simply don't seem to have any other answer. But.. they aren't so fun to debate with. But, when folks can respectfully debate and discuss matters, it's the best.
Primarily for arrogance & for deep rooted superstitions. Religion begets intolerance almost as a rule. It's not amazing that people who believe his, or her, interpretation of god is the ONLY correct one; that he or she alone, somehow, has stumbled upon the identity of a one TRUE god, while all the other creeds, believers, non-believers, ministers, priests, scholars, infidels and atheists have misinterpreted, and misunderstood, the truth about god, are opposed, offended and intolerant to alternative ideas & beliefs. These people sincerely believe & act upon the utmost fallacy that "if you are not with them, then you must necessarily be against them"! Hence, for the acute lack of truth, logic & reason, they persecute, threat, scorn & bully like their spiritual ancestors. Whenever they fail to reason, they resort to hatred & meanness. They forget that such actions only portray the inherent weakness & obvious absurdity of their faith!!
My reposted answer from another similar question...
Truth is often found in the extremes. Take religious fanatics...please. They have incorporated their religious beliefs into their self identity to the extent that faith in the supernatural and self are inextricably linked. It is why Jihadist and abortion center bombers are able to do what they do. To even suggest that their belief system is faulty is, to their mind, comparable to a death threat. They cannot see their life as having meaning without faith. But that is the extreme. However, it has been my experience, having been on both sides of the theistic debate, that most true believers, regardless of the level of their commitment, will hold some degree of this same self identity which carries a comparable degree of resistance to questioning. Hence, religious debates seem to always devolve (usually rather quickly) into accusations of hatred by those who feel threatened when their core beliefs are called into question. In other words, one cannot question and simply be referred to as someone who "disagrees". They are referred to as "haters". It is the black and white world of true belief.
One man's truth is another mans insult. One man's way of life is another's squandery of it. One man's trash is another's treasure. And if an all knowing entity does not see or understand everything then that entity will deny the truth of the thing it does not see or understand. This can be offensive. When you tell a person they are doomed because they wont believe what you believe this is offensive. When you tell a person what you believe is the absolute truth it comes off as arrogant. And when you arrogantly assert or superimpose your rules on another's universe it looks selfish. And when people think your deception is what you consider help it usually makes them angry. The truth is that the discussion of religious views has intrinsically bad manners accompanying it. It is the only way people can manage because it is what they have been conditioned to BELIEVE is the 'right' way to compose their lives. It's not anyone's fault but the process MUST look as though two wolverines are going at it because the basic expressions of faith are impositions and naturally people get offended by this. The only other option is to submit to a new paradigm which is not most peoples first choice.
Because people don't seem to understand that we're all here, and we're stuck working together. People spend so much time arguing while the Earth is slowly dying. They waste time that could spent productively. I may argue about things at times, and inadvertently get nasty, but I don't aim to force anyone to change. Just to think a little. Sort of like Socrates (except hopefully never being put to death).