They are probably just wondering "Why should I defend evolution? I'm no scientist, I just believe in one less god than you do. And what does evolution have to do with right and wrong, anyway?"
Regardless of evolution, I get my sense of right versus wrong form my parents. They taught me that: Things than hurt/harm others or cause people needless discomfort, those are WRONG. Things that help people, make life easier for them, things that make others happy, things that makes other people feel good, those are RIGHT* things to do.
Refusing to contribute to society, by not paying your taxes, that is WRONG.
Respecting other people's choice of a significant other, as long as they are consenting adults, that is RIGHT.
* You noticed there that there was nothing about "Things that make things easier for ME, helping ME getting richer, getting ME higher on the ladder", in that list, right Kenny? Those things are not RIGHT, those are EGOISTICAL things.