Our western European allies are taking a shit-ton of these refugees, and they really don't have a choice since most are just showing up (similar to many of our Latin American immigrants that are here to escape poverty/drug cartels). Agreeing to take some on helps our allies, which makes them more likely to help us with other issues (i.e., fighting terrorism globally and taking our side in disputes with Russia and China).

But the reality is there is not always a purely "practical" way to look at these issues. The situation in Syria is currently the biggest humanitarian crisis in the world. 99% of refugees just want out and a chance for a better life. There will be a very small percentage that are radicalized and/or have the capacity to become radicalized. Of course we have this risk with American citizens as well. We've all heard the terrible "poison M&M analogy". The problem with that analogy is these are real people undergoing real suffering...not inanimate pieces of candy.

The reason this has become a liberal vs conservative argument is similar to the reason gov't assistance for poor Americans is a liberal vs. conservative issue. In general, liberals are OK with gov't policies that help poor people even though they get nothing out of it themselves. Conservatives don't want any government policies that could be negative to them even if it could help others.