If I know somebody is wrong, then I tell them if I can. I do so in person as well as online. I don't think it's disrespectful at all. I've debated Christians in person as well as online. None of those Christians were hurt.
I've told Christian apologists that the best apologetic is for them to give a good example of just how sensible, informed, and moral a Christian is due to their beliefs. As far as I know none of them have taken up that challenge.
I'd prefer a world where tolerance and good works are of primary importance. I really don't care if others believe in the supernatural as long as these beliefs are a positive influence, leading them to be more charitable.
One of my biggest concerns about religious belief is the adverse impact it can have on education especially science education. Living in a society full of uninformed and misinformed people can't be a good thing if education has any value at all. So I do care if any kind of thinking or lack of thinking results in millions of superstitious, ignorant people.
I don't see much point in debating the immoral, repulsive type of Christian as it's almost impossible to bring someone out of a life long cult. But, if an atheist wants to take these people on, go for it.
Since I don't really know who is a hopeless case and who isn't, I take on all comers. Even if a "hopeless case" won't listen to reason, some of those looking on might well listen to reason.
Some people don't feel comfortable debating or having to defend themselves.
Evidently some atheists feel that way, and that's why they objected to my debating Christians. They may have feared that they would be proved wrong too.