"You could argue Brits did not choose to have their abnormal sensitivity to salmon while Muslims might be considered to be choosing their sensitivity to Mohammed. But this requires a libertarian free will. "

Absent free will I don't understand why you'd be more critical the supposed offending parties than the offended ones.

"And if tomorrow I tried to "choose" to become angry every time someone showed me a picture of a salmon, I couldn't do it - I could pretend to be angry, but I couldn't make myself feel genuine rage."

Some people born and raised in America who freely take up Islam in adulthood and proceed to take offense at such things as pictures of Mohammed which they previously would not have taken offense at. One may not directly choose to take such offense but it's a consequence of choices and one may choose otherwise.

Out of a billion muslims I'd bet there are many who are not deeply offended when outsiders print such pictures. The choice to take less offense is there.

Growing up I had a strong and deeply ingrained aversion to homosexuality. I could feel physically ill at the description or depiction of men kissing, for instance. The aversion was so strong that I identified it as an instinctive part of my nature. Over time however I chose to discount the aversion. I was able to do so. Presumably you would not have thought gays should have refrained from acts which offended me.

I'm confident muslims are also capable of discounting irrational beliefs. If one didn't think people could do this then what would be the point of lesswrong?