Quite true, but the religious often defer to the rule book when making moral decisions, rather than analyzing the actual effects a given decision might have on others.
Case in point: anti LGBT attitudes.
I'm not sure that's always true even for the most hardcore by-the-holy-book types of religiously motivated morals.
Take, for example, the stereotypical "Do X/Don't do X or you will go to Hell" - wouldn't that be, essentially, a consequentialist argument?
Why are mixed fabrics forbidden?
By my understanding, most of the rules in Leviticus were regulations intended for priests of the Temple. Doing certain things would make them ritually Unclean and therefore unable to perform the necessary rites and duties. As far as I can tell, this principle was fairly common among Levantine and Mesopotamian religions: To perform the rituals of their faith correctly required the performer to be in the correct state of mind and body, and any variation or flaw could potentially anger God/the gods and cause the ritual to fail.
So to answer your question in that spirit, "because they make your soul filthy, preventing you from performing your sacred duties, and potentially putting your entire community in spiritual or physical jeopardy".