I think the problem with pork is that pigs will happily eat and root in human waste. This means human parasite eggs and larvae end up going back into our food chain when we eat the pigs. That's what makes them 'unclean'.
Labeling pork 'unclean' is just standard operating procedure where arbitrary restrictions are introduced to generate an "us vs. them" divide and give the religious authorities more control over the everyday lifes of the believers.
Same dynamics as when religions take great interest in the sexual lives of the belivers
Going on how your comment has been rendered invisible, looks like you triggered someone :]