Again, not defending white supremacists by any means here (I keep saying this because sometimes it's uncomfortable playing devils advocate...)
Considering the statistics, I am sure there is a higher percentage of White Supremacist that turn to violence compared to Islam
I'm not aware of any such statistics, and I would also argue that moderate white supremacists (i.e. your everyday racist white guy) are far less likely to self-identify compared to muslims.
I would also point out that religion in general is often pretty racist too...Jews in the bible proclaimed that they were a special race, to name one obvious example. Even when the holy books aren't explicitly racist, the doctrines are often so intertwined with racism that it's difficult to separate them, at least historically speaking.
However, we are still a society where such religions are considered the norm.
That's my main point for those that would defend islam regarding it's connection to terrorism. The only thing that separates it from other disgusting ideologies is that it makes supernatural claims and calls itself a religion. It's no more racist to criticize islam than it is to criticize white supremacists. It's just pointing out the obvious.