Why religion is a bad thing

Because they promote Absolute Truth
Because absolute truth mean absolute arrogance
Because absolute truth means absolute deafness
Because they promote blind belief
Because blind belief means blindness
Because absolute truth justifies absolute actions
Because it disencourages critical thought
Because has always been a great excuse for war
Because it allows the demonizing of enemies
... and demonizing is the first step into deshumanizing
... and deshumanizing eases killing: not human -> can be killed without remorse
Because, many times, it promises some better life after life on Earth
Because it makes life on Earth less valuable
Because it's easier to kill someone if you think he is going to a better place.
Because it's easier to kill oneself because one thinks there is a better place.

Yes, there is another life, that has nothing to do with oneself. There is worms, plants, fungi, microbes, which can happily grow among our rotten flesh.