"It is really the single most basic idea about religion, that it marries itself to whatever culture it comes into contact with.”
In terms of honour killings, for example, the main problem is that Islam - or, more correctly, the Koran, the sunnahand the hadith - are full of references to 'honour' and the concomitant need to abide by the 'principles of honour'.
In sharia law there's also the notion of 'ird. This applies to the honour of the individual Muslim. Abdul Wahid Hamid (in his Islam the Natural Way), for example, writes that
"preserving honour... is the goal of... sharia laws that punish sexual relations outside marriage'. In addition, the 'severe punishments' of Sharia Law are there to 'protect honour and chastity (125)”.
"problem is that you’re talking about a religion of one and a half billion people, and certainly it becomes very easy to just simply paint them all with a single brush”.
1) ".... Islam is largely a process of Arabization, so to speak. The teachings and practices of Islam stem from those of the Arab desert culture from which Mohammed came...."
True to a point. Islam is still indeed Arabic. Though Arabic culture became Islamised too in that it can't be denied that Muhammad brought things to the Arab tribes which they would have been unfamiliar and unhappy with.
So Muhammad "married" himself to Arab culture. (He couldn't help but do so - he was an Arab.) Then he created an Arabic-Islamic culture and society. From then on, all Muslim societies married themselves to Arabic Islam; rather than the other way around, as Reza Aslan suggest.
After all, it's 2014 and the vast majority of non-Arabic Muslims still have both Arabic first names and Arabic second names. Many still wear Arabic clothes. Allah is a monoglot who only speaks Arabic. And the Koran "can only be truly understood in the original Arabic"... and all that's to miss out the many abominations of Arabic sharia law.
2) "Rather, the truth is that Islam affects local culture and local culture affects the practice of Islam."
I hope I didn't come across as going too far in the opposite direction to Reza Aslan - completely denying local culture or "material conditions". Marxists called that position both "idealism" (the philosophical position) and "voluntarism" (i.e., the - complete? - psychological freedom from material conditions).