The Argument for Islam is very Simple:

[Crunchy]

The Argument against Islam is very Simple:

1. The founder was a sex slave owning murderer, rapist and pedophile.  Don't revere that.

Actually the "founder" is as phony as a $3 bill.  What that means of course is that the slave-owning, murdering, raping, pedophiles who invented him wanted someone after their own hearts!

Something to think about when dealing with barbaric religions.

Or maybe that an actual leader arose from that community. It's not much of a stretch.
Many barbaric cults were actually founded by actual founders. The historical consensus is that Muhammad was a real guy regardless of any fashionable theories to the contrary. 

However, when evaluating a religion this is irrelevant as all that matters are the writings the believers revere as there is nothing else to go on. Arguing with believers that their guy was probably not real gets you nowhere as the holy texts are most certainly real.
Christianity is what it is regardless of whether or not Jesus actually existed. So, whether the words sprang from someone named Muhammad, or from some other guy(s), the outcome is the same.