The fundamental difference between Islam and virtually every other world religion is that in every religion EXCEPT Islam I can dig into their holy texts and find support for theological arguments against "conversion by the sword" and "murder of unbelievers".
So yes, all religions have at one time or another had bad people that twisted the tenants of the faith to serve evil purposes. Only in Islam is the evil hard wired to its core.
As for why the institutional left in the west seems to always look the other way at the sins of Islam? Its nothing more complicated than "The enemy of my enemy is my friend". Islam's enemies are Christianity, Capitalism, Western Civilization and Israel ... the same enemies as the left.
It helps that Islam is actually a political system masquerading as a religion ... a political system that has a LOT in common with Marxism.
If you have a lot of time on your hands and have always wanted to read The Qur'an to find out what all the hubub (or in this case habib) was but you're not looking to learn Arabic and convert to Islam first, I recommend reading Robert Spencer's Qur'an Blog wherein he reads the book from cover to cover and discusses it (start at the bottom of the page and read up if you want to read it in order).