peaceful - re "there is no leadership in Islam so the interpretation of the radical violent Muslim groups is just as valid as yours"
The idea, as I remember it, is that Jesus didn't establish a Church & appoint a Pope, and God was very disappointed to see it happen. So when he sent down Islam, he made it clear that the religion was between each man and God, with no need for an institution or leader in the middle.
I happen to think that is a good thing. If there were to be a Caliph in Islam right now, it would probably be someone like Khomeini or some Saudi prince. Where would the moderates and progressives of the world be, then? They would be called "heretics".
"one of the negative consequences of the ending of the caliphate system is that it is more difficult to police the Muslim world and deal with radical, unorthodox interpretations"
One person's "radical, unorthodox" is another's "normal". I honestly think it is a good thing that nobody is "policing" anyone's religion. If there has to be religion in the world, everyone should be free to practice it as he/she sees fit.
"He (Ali) just dealt with them headon and wiped them out. Today would be impossible for Muslim governments to completely get rid of them because they cross over to different countries to operate so fall under lots of countries jurisdictions."
That wouldn't change if Islam had a Caliph, since he wouldn't be able to order a strike into another country.
"I know a lot of westerners support the Syrian regime because they are afraid of 'islamists' (whatever on earth that means) gettIng to power."
I am really in two minds over this. On one hand, a dictatorship is not a good thing. On the other hand, nobody deserves to have their country run over by a band of ignorant misogynists from the Dark Ages, like what happened in Iran after the Shah or Afghanistan after the Soviets.
I can't decide which is worse. In fact, I think I'd rather live under a dictator than in Saudi Arabia or Iran.