"This is my covenant, which ye shall keep, between me and you and thy seed after thee; Every man child among you shall be circumcised." -- Genesis 17:10
"...if ye be circumcised, Christ shall profit you nothing." -- Galatians 5:2
This is a classic example of someone who simply doesn't understand the message and most likely hasn't even tried to understand the message.
In the Law of Moses Jewish boys were required to be circumcised in keeping with the promises made with Abraham (as quoted above). In the New Testament believers are told that there is no need to be circumcised NOT because circumcision is wrong, but because the teaching of Christ goes beyond it.
In Galatians Paul is talking to people who were rejecting the teachings of Christ and going backwards. That's why he said what he said. Th fact is that Jesus said that he didn't come to destroy the Law of Moses - but to fulfil it, and that Paul in some circumstances actually went and carried out circumcision! So the contradiction is not a real one.
Harmonising those two passages is very straight-forward but only if you're actually interested in doing so. Seek and you will find. Close your eyes and all you'll find is the inside of your eyelids.