I don't think CHRISTIANITY makes people worse, I think sin does.
As a broad generalization, I think Christianity tends to have a positive impact on people. It's hard to give what we don't have, but Christian have mega doses of unconditional love, forgiveness, grace and mercy - all good things they are now able to give and share. And I think Christians have a model of love, service, care and sacrifice. And I think Christians have a view of loving morality and the strength to move forward in such. IMO, this often does impact and change people: I can witness this a bit in my own life.
Now, does that FORCE Christians to be "better" than their pagan neighbors? NOT NECESSARILY. Indeed, since all we can witness is what is said and done (not the heart behind it), it can appear (and may well be the reality) that Christians are often no better than non-Christians. Theologically, this is not hard to embrace. Our justification is in view of JESUS, not us. And Sanctification is a life-long process that is synergistic, a reality that we have TWO natures - the old Adam continuing.
Collectively, socially, I think it should be said that politicans are at times outstanding at abusing religion, using it as a tool for their own political ambitions. This has been true in Christianity as well as in other religions. Religion is a powerful force in people's lives and power-seeking people have learned to "tap" that.
FUNDAMENTALISM is a force in many things - including religion. Fundamentalism is a radical form of belief (whether political, religious, cultural or otherwise) and in this radical form, it becomes irrational and passionate and often takes on an ugly, "anti" element. Consider the nationalism/Ayrianism of Nazi Germany. We find this in Christianity, too.
- Josiah