Religion doesn't work that way. You don't go "Well, I have this set of values, so I think XYZ is the right religion for me". There are exceptions, but most of the time it's actually exactly the opposite.

If one facet of someone's faith is enough for you to dismiss their entire belief system, you clearly don't even try to understand others' differences to yourself...

Oh, I try. But in the case of organ donation, I simply fail to understand the reasoning. If you're dead, why not save a life, renew sight, or otherwise greatly improve the life of another? Are there people who think that organ donation would hurt them in an afterlife? We, at least in the first world, live in societies with freedom of conscience and belief, so people should at least think through the consequences of their choices on others. (And on themselves; if there's an afterlife, do you really want to risk being judged on the basis of having chosen to deny a chance at health and wellbeing to another person?)