John P, please correct me if I have misread your post but you seem to be equating involvement in politics with corruption. You are absolutely right to condemn the buying of influence, but one can engage with the democratic process in a perfectly legal and moral way. I would argue that, because religions are all about people, they have a duty to get involved in politics.
As regards the point of Catholicism I suppose the basic answer is that, as with other religions, people find a need for it. One could argue that such a need is rooted in self delusion, indoctrination or whatever but there are over a billion Catholics and I remain to be convinced that they are all in some way deluded.
The church has been around for a long time and I am not in a position to say whether the world is better or worse for its existence. I do know that most Catholics of my acquaintance make a positive contribution to their communities. I also know people who have no faith and make equally valuable contributions. I am not sure what one can draw from that. It could be argued that if all people lived their lives in genuine accord with gospel values and never offended against those values the world would be a much better place, but we are all fallible and that's never going to happen.