Why are Many Rational Atheists So Dogmatic About Evolution?

I get that many theists can become strongly passionate about their religious convictions and connection to God or Gods, but from my personal observation (online at least), a lot of atheists resort to dogma when it comes to discussing evolution. But why?

For instance, when questions of skepticism about evolution appear, there is a strong tendency by some atheists to go into attack mode and defend evolution at all costs. In most cases, discussions begin with snarky remarks, ridicule, jumping to conclusions about what the person is or isn't, questioning the intelligence of the questioner, etc. Not to mention the whole "You don't understand how [fill in the blank] works".

Somehow, someway instead of addressing criticisms or questions with sound, reasonable answers that elevate the discussion and solve problems, conversations with dogmatic atheists degrade into immature, irrational, small-minded squabbles over religion (specifically creationism) for whatever reason and the discussion becomes about the questioner's understanding, character, personal life, etc., and not about the actual question being asked. Or, instead of answering the question, the dogmatic atheist will rebut with a question that casts doubt on the questioner's ability to comprehend information.

That sort of defensive response only presents itself in those with a religious conviction. It isn't what someone unbiased, reasonable, and mature-minded does.

Why be hyper-defensive about evolution if evolution is an accepted theory of science that is self-evident and self-sustaining? Why are questions about evolution met with criticism of the questioner themselves? Why not just answer the question instead of getting "religious" over what you say is fact?

Besides, self-evident facts need no defending or protecting ... They should be able to stand on the merits of their basis in reality. If evolution is self-evident, why the dogma?