Convictions

I hesitate to write this because I'd really like to get some responses, and obviously I'm not a "higher being" in the flappy world of blog ratings! But it's something that I think about often, and maybe someone will have great insight.
I don't understand why so many believers have different convictions. I know that in many cases believers are being called to live more seperate lives than we have in the past few generations, and many of us are very likeminded in the way we see the true "american dream" lived out, but still- there are those little convictions that separate even those of us who are otherwise generally like-minded. The most prominent illustration from my family: we think it of great importance what we put into our bodies. It isn't a biblical mandate that we all watch what we eat, although the Bible does speak to how we should take care of our bodies. But my husband and I believe the way God laid out His plan in Leviticus is indeed the best for us. For example, studies show the unclean meats determined so by God have a higher toxicity than the clean meats. We all know pork is an unclean meat, read this link to see why. Didn't God have our best interest in mind when He set up the law? I am not saying that we are obligated to follow the law. Jesus fulfilled it, but He didn't abolish it either. I believe, with science to back me up, that God set out the perfect health plan and we should do our best to follow it. Why are we convicted to eat healthy when others haven't even *thought* about reading the ingredients list?
Convictions are a mystery to me.
(yes, I still eat ice cream!)