Quite a few people who oppose abortion also believe that emergency contraception commonly operates by killing fertilized eggs (by preventing implantation), whic

Quite a few people who oppose abortion also believe that emergency contraception commonly operates by killing fertilized eggs (by preventing implantation), which would qualify as abortion under their definitions. If that is your belief, and you believe that abortion is morally equivalent to murder, then banning emergency contraception would be a self-consistent thing to do. (Now, the studies I've seen suggest that emergency contraception does not often if ever work that way since it appears to be entirely ineffective when taken after ovulation has occurred, but that's a separate question.)