It's an internet phenomena that relies on anonymity. The troll is like a con man. The con man runs about stealing money from trusting people and by doing so he thinks he is above, more cunning, and far more intelligent than the average person. Each time he takes his mark for a bit of coin he imagines himself to be powerful.

The problem with the con man is that we pity him. Life is one big con. Even his closest friends are out to take something from hi,. He cons people because he lives in a world without trust. "There is no honor among thieves."

The troll runs about attempting to be witty. By doing so, he imagines himself to be more intelligent and witty than the average person. He never understands the fact that wit or the sly remark are not measures of intelligence. He is either afraid or unable to be honest. His world view is one of trolls. The people who value him and his wit are other trolls. His friends troll him and he trolls them. This is the world he lives in. Like the con man, the troll is to be pitched for the world he has created around himself.. A bit of wit can be an asset to an intelligent mind or a ball and chain to the ignorant.

By trolling, the ignorant never have to take responsibility for their own ignorance. They feel intelligent and superior in their ability to get an emotional reaction out of others. They live for posts like the one you have made. "Look, he is talking about me. See how powerful I am." This is the mindset of the troll.

If we were Christians, we could pray for them. That would be the same thing as doing nothing at all. And sometimes, nothing at all is the best thing you can do. When you see a troll, just avoid them. Lacing responses, those things they need to feel good about themselves, they will move on. They only need one victim to feel validated. Don't be that victim. "Whatever/" Is a great response to a troll any time you spot one. The less you give them the better.

I have explained this before. From time to time some ambitious youth minister gins up his youths to seek out "sinners' (non-believers) to "convert". It is a project a task or just something to do. They call it "god's work." They use a myriad of tactics in this "operation." One is to pose as a student that wants to understand atheism and that they are "writing a paper for college." I strongly doubt that they are in any credible college. Anyway, they pose a question like: " Why don't atheists accept the fact that jesus is the true god?" A loaded question to be true. It is also a "push-poll" question, meaning that the outcome is predetermined. When we atheists reply to said question the response by them is a series of biblical quotes proselytizing and preaching. These youths are inexperienced in actually discussing or debating with educated people about anything. They are woefully lacking education and information about the bible, history, science, and almost anything, especially reality and facts. Thus their frustration and anger. On the other hand, the youth minister is surely pleased with causing disruption of atheist forums by sending his minions on trolling missions. christians are by nature vindictive and hateful.
Another type of troll monster that visits atheists sites are the Youtube self-promotion characters. Their mission is to drive people to their websites to get publicity for their YouTube video and gain recognition in the christian world. They score points by angering atheists and disrupting any form of communication or conversation that isn't an obedience to respect obey and recognize their god. Hence "the yellow post."
Usually, they are just drive-by attacks. A few blurbs and then they are gone, but sometimes it is a prolonged rant even continual spamming.
christians are the worst sort of people. They like to dish it out but they can't take it. They pose as innocent people and also pose as "victims". Of course, they are the aggressors. Even they know that, even though they would never admit it. They see any crime or violation as justified because they are "doing their god's work".
It's actually fun to blast them out of the water. To shake them to the very core. They run away as fast as they can as soon as they realize that they are in the deep end of the pool. They can't handle facts, history or science. They are basically naive and insecure, stupid ignorant and uneducated. Which is the reason that they are christian in the first place.
My advice is just to enjoy yourself by blowing them away as soon as they appear. Oh, and BTW, they absolutely cannot handle profanity. Which is hypocritical since from their very first post they are insulting.

This may sound trite, but the answer is simply, because its's the internet.