Suppose the doctor told you that you had lung cancer. Would you feel content to ignore his diagnosis if you found out he was a smoker? Of course not. Why? Because the fact that he is a smoker doesn't change whether or not you have cancer.
Or let us suppose for a moment that the atheists have it right, and there is no God. No supernatural realm exists. Would God suddenly spring into existence if atheists began acting like a bunch of arrogant jerks? Of course not. Why? Because the way atheists behave doesn't change whether or not God exists.
Finally, suppose that no Christians were hypocrites. Would that, by itself, make Christianity true? Of course not.
I hope you can see the point I am trying to make. The claims of Christianity are either true or false. And they are true or false independent of how Christians behave. Sure, it is deeply troubling that people (like me) who claim to follow Jesus behave badly (although that is actually consistent with a Christian view of humanity--we are all sinners and continue to wrestle with the flesh), but that does not make the claims of Christianity false.
I would like to make one other brief observation here. I think that this objection reveals a serious problem with the way Christianity (and truth in general) has come to be viewed in modern, western culture. Christianity is viewed less as a set of claims (about reality) and more as a commodity. On this view, it doesn't even matter if the claims of Christianity are true or false, because people are decreasingly interested in truth and increasingly interested in utility. I don't care if it's true. What I want to know is, does it work (for me)? Does it do what I want it to do? If so, then it is worth owning. If not, throw it away. That might be an appropriate way to approach purchasing a cell phone, it is a terrible way of deal with claims about ultimate reality.