Christians often let, or even encourage, materialist atheists to fall back to a kind of meaningful moral realism. A kind of 'You may not believe in God, but surely you believe in goodness, right? Charity? Kindness? Doing good, improving the world?' compromise. I think there's a number of motivations here - a belief that that inner conviction of 'goodness' may lead atheists back to God, a general hope that an atheist will at least still do pragmatic and beneficial things. Plus, the general unwillingness to assert that a convinced and willing atheist cannot really be doing 'good' from their own perspective, given how rude and unpopular that view is.
My view: letting a materialist atheist pretend that they can still talk meaningfully about 'good' and 'evil' is likely to do more harm than good, from the Christian perspective. It's encouraging people to be zealous with no real anchor - hence, SJWs.
Let me be clear here: I'm talking about materialist atheists. I don't believe agnostics, or the merely irreligious are in this boat. But once someone talks about how the natural/material world is all that exists, etc, acting like their logic-pretzels of trying to pretend they can pull 'rights' out of their ass and that this means something has to end.