I’m a liberal, but I can only speak for myself and my own feelings. Also, I’m from the US, and I only know American Muslims, so I’m primarily thinking about them in the following.
I certainly do not call anyone bigots, unless the definition unequivocally fits (like with the KKK).
I feel drawn to defend anyone who I feel is being unjustly ganged up on. After 9/11, a lot of anti-Islam attitudes suddenly popped up, and a lot of innocent Muslims were affected by this prejudice. I suppose its the same sort of thing that happened during WWII to Japanese Americans (though not as bad in this case, fortunately). At least as practiced in the US, Islam is generally a harmless, peaceful religion, and Muslim Americans just want to go about their business, practice their religion, and not be harassed. They didn’t like Osama bin Laden any more than the rest of us did. Even on this board, which usually has a higher standard of behavior than most internet forums, there is far too much uninformed anti-Muslim rhetoric. So, I feel drawn to defend them.
I know only a bit about Sharia law. There are some parts that I find praiseworthy, some parts that I find appalling, and some parts that I’m neutral about. In general, I don’t want to live under Sharia law. But, I don’t mind if US courts need to refer to Sharia law,
No Muslim American that I know of wants to impose Sharia law on the US.
In summary, I defend Islam because I see that it needs defenders in the US. If I lived in an Islamic country where it was the Catholics who were being oppressed, then I would spend more time defending Catholicism.