Brownie,
Discussing the relative merits of boots or skis is one thing. As you are finding, discussing issues that are rooted in our deepest held personal beliefs is another.
Here are a few things I try to keep in mind when entering such discussions. I can't say I always succeed, but I do find these rules to be helpful.
DEBATE IDEAS, NOT PEOPLE - None of us is really expressing new ideas. We are really mouthpieces for traditions and lines of thought that have been handed down to us. Unfortunately, ideas need people to express them and people are clumsy. Old joke: How do porcipines mate? Carefully. Focus on the ideas, not the quills. When you a post, look for the idea that is being expressed. If you see personal attacks, you have lost focus.
NEVER, EVER PERSONALIZE - Electronic communications is turbo charged with emotion. Just the nature of the beast. Work very hard to avoid making personal assertions about other posters but recognize that no matter how hard you try, somebody somewhere will take personal offense to what you wrote. Going the other direction, ignore personal attacks made you against you at all costs. You find when you meet over beer/coffee/whatever that most of the personal attacks weren't meant. People type and read without the aids of body language and feelings get hurt easily.
LET YOUR IDEAS DEFEND THEMSELVES - The only times I've seen people's minds changed on deeply held beliefs based on internet discussions is small, non-public forums and even then, these changes take years to evolve and are very, very rare. Resist the urge to convince others to join your point of view. At the same time, be confident that the ideas you express have a power of their own that will make them capable of defending themselves. It is helpful to remember that while the person with whom you are discussing/debating ideas with won't change his or her mind, others who read and lurk will be considering the merits of your ideas. CS Lewis said that you defend God like you defend a lion. You unlock the cage and let the lion defend itself. The principle of HYOH (Hike Your Own Hike) applies here.
DON'T TAKE THE DEBATE BACKCHANNEL - IMO, it is folly to think that anybody will change their mind based on direct confrontation over electronic communications. Resist the urge to take debates to PMs, feedback quips and e-mail. This cuts both ways. 99% of the time, negative PMs, e-mails or feedbacks that you receive are motivated to get you to change your mind. Ignore the bait.
BE WILLING TO TAKE ONE FOR THE CAUSE - When you step into discussion of ideals, you can be guaranteed that somebody will disagree. When you do this on electronic forums, you can also pretty much guarantee that somebody will disagree with you in an inappropriate manner. This is simply the cost of doing business. You have 2 choices here. First, is the idea you hold dearly important enough that you are willing to voice it while knowing that others will disagree? Second, can you sleep at night and ignore inappropriate personal attacks made against you in public? Different people will have different answers.
NEVER WRESTLE WITH PIGS - It is amuses the pig and makes you look bad. No matter how polite and tactful you try to be and no matter how hard you try to avoid personalization of attacks, you will occasionally run into people who will just be totally unreasonable. My best suggestion is to ignore them entirely. Never respond to their posts.
I should close by repeating that these are rules that I try to follow. I don't always succeed and you would have to be a robot or saint to be entirely dispassionate in these situations.
I hope some of this is helpful for you. You've given voice to some important ideas.