Just to add, part of the problem I have with people always using their religion to defend an argument is that in doing so one implies, of their own volition, that their religion and their religion alone is the one "right" religion and all others are wrong. That's a rather presumptuous and arrogant approach to take, don't you think? Let me expound on what I mean by this.

If we started a discussion on whether or not abortion is "humane", invariably religion (and by religion, here, I mainly am referring to Christianity) would be brought into the debate. The problem with that is, if you're going to say how something should or should not be (as in a law) then you can NOT use religion as a means of your debate. All the anti-abortionists of the world would be doing themselves and their goals a huge favor if they put their religious views aside in effort to defend their argument. You want me to understand why circumcision is acceptable or unacceptable? Great, but we don't necessarily share the same religious views so do me a favor and convince me without using your beliefs as a source of debate. Otherwise, the only people you're speaking to are the people who already agree with you (and there's no point trying to convince them if they already believe you to begin with, no sense in preaching to the choir.)

If you want to convince people of all walks of life (of all religions) to accept something as ethically and morally "right", then you need to back up your reasoning with logic and proven fact, not: "Verse XX:XX from the Bible states thou shalt not..." Because let's face it, not everyone is Christian and suggesting what should or should not be permissible because ONE religion dictates it, well you're essentially making yourself an imperialist dictator. Thank god (no pun intended) for separation of Church and State! If the pro-lifers of the world had their way, we'd all be bent in abject prostration with the Christian will forced upon us. For that matter, anyone who backs up their argument with religion falls under the same category (whether they are consciously trying to or not).

If you can win an argument or make a solid defense feasible without religion, then you are able to address all people without discretion. When you start bringing religion into the picture you instantly limit your audience (not to mention your credibility).