"Atheists have lots of problems with Christians. "

Christian Athiests don't.

"Atheists think (mistakenly) that this illusion we are in is all that matters. "

Of course they don't.  Notice how much I've been talking about the 'illusions' that will follow this 'illusion'.

If you have an imaginary creator god (who would be responsible for creating suffering), you might try getting him off the hook by:

1. Pretending that suffering doesn't exist, which is absurd.

2. Calling suffering 'an illusion' to suggest that it doesn't count somehow.

Whether it's an illusuion or not it still hurts, and to ally yourself with the imaginary divine torturer is evil indeed.  Luckily, there is no super-criminal such as the one you worship.  Unluckily, for everyone who has to live in this world with them, there are sick people who want to ally themselves with a divine torturer. 

Merely using the word "illusion" doesn't affect the following:

Since suffering exists, there is evidently no one with both compassion and omnipotence.

"People who think that life has no purpose have only defeated themselves."

I agree.  It's people who believe in a creator god who think life has no purpose.  They think that all they have to do is join the club and then the purpose of life is accomplished.  They think they can cause any suffering they like and they won't themselves have to suffer later (their idol is a toturer, after all). 

They're in for a big surprise!