Both sides, left and right have their opinions on Islam. The left generally will promote it and the right will generally either be neutral or discourage it. Each side has their own motives and reasons for their positions, but looking at the problem objectively, what is the truth?
The truth is that the two sides are usually talking about different things when they espouse pro or anti positions. A pro position will usually focus on the people, the individuals who are religious and otherwise normal. These people could adopt Western political theory because they have not politicized their religion. An anti position will focus on the propagation of islamic political ideology. Some Muslims in the Western world have not adopted the Western schools of political thought. An anti Muslim position will usually not be directed at the individuals, but at the political and legal theories that some Muslims promote which are incompatible with Western political thought.
Islam becomes a problem when it is used as a legal system. Being a Muslim, when practiced solely as a religion, is not any more wrong than being anything else. Islam only becomes a problem when it is used as a legal system for society. Sharia law is incompatible with the West much in the same way that fascism and communism were found to be incompatible with the West.
Much like the fascism that was defeated in Italy and the communism that was defeated in Germany and Japan, Islamic Sharia is a totalitarian expansionist ideology that has many followers who are willing to fight and die to expand their influence. That is why it is so important to say the words; "Radical Islamic Terrorism", because we must recognize that the threat is not a religion, but a political ideology that stems from a religion.
This is an ideology that has no reason or motivation to stop expanding. Why would they when it is one of the tenets of Sharia to expand? This type of political ideology is something the US has seen before, and something that the US has decidedly defeated before.
The left is correct in wanting not to stigmatize individual Muslims, but they are wrong when it comes to the numbers of Muslims who subscribe to Sharia law. There are certainly many individual Muslims who promote the spread of Sharia law. These are the Muslims that the right denounces and rightly so.