Chris. Answer this question.
Do you think it should be illegal to protest a funeral? Yes or No. And if you really have to put qualifications on that......therein lies the problem with you and me (in our ideology).
Alright I'll be the one to say it:
It should not be illegal to protest a funeral. Or for that matter, a bar mitsvah, a christian christmas play put on by kids, a gay pride parade, a gun show, or a wedding. People have the right to their opinions and the right to express those opinions in peaceful ways, even if that pisses you off. These people are expressing their religious views, and while I'm openly an athiest and think all religions are crazy, i fully support everyone's right to believe what they want to believe and express that belief.
For the record i would protest a funeral if i was really opposed to the person. Say the lockerbie bomber who got the bullshit compassionate release despite killing hundreds of people. I would protest that. Maybe I'm an asshole for it, but that's my right, just like its your right to call me an asshole.
You can claim that your legal system would be result in a better society because it would prevent extreme assholes, but aside from the easy to make slippery-slope argument, I think you have already detracted from society by making these assholes illegal. Your public discourse is no longer real because you have made some opinions illegal, or at least the peaceful expression of those opinions. Your society would never have the opportunity to band together against these guys like the motorcycle gangs who drown them out, or the groups who hold hands to block them.
Making speech illegal because it offends you is not only a weak way to avoid the issue, but it conveys fear of the speech (not saying you personally are afraid, but the laws would make the government look it). If the speech is so illogical, then beat it fair and square with discourse. Your ideology leads you to drawing a subjective line to decide what you personally consider too offensive, and that your shared government should intervene with force to prevent those people from offending your ears any longer. That, in my opinion, is immoral.