The fact that people fail to live up to an ideal does not mean there is necessarily anything wrong with the ideal. It does mean that there is something wrong with us, though. Jesus was pretty straight with us about our shortcomings. God is perfect and demands perfection, but none of us live perfect lives; all of us are screwed up.
If we could get our act together, then Jesus would not have had to go through the pain and humiliation of His public trial and execution. Instead of just telling us to grit our teeth and try harder, Jesus told us we needed the forgiveness and power that His death and resurrection bought for us. It is because I can't live up to the ideal, that Jesus did all that He did.
Jesus also told us some people would try to use His name to justify their selfish acts. We don't need to look far to see those abuses. But we shouldn't allow the errors of others to disqualify us from the good that Jesus can do in our lives. Taking time to read the gospels helps us see how far those who have tried to use Jesus are from Jesus Himself.
Everything good can be used to evil purpose. Are we going to let other people's abuse separate us from the good that Jesus can do in and through us?