I would say that there isn’t a causal link. What I would say is that they are enabling us to become more polarized. The same political behaviors we have been exhibiting since forever are what are causing us to become polarized; the environment is what enables us to be more or less polarized compared to other environments.
I can remember reading some research* nearly 20 years ago that observed increased polarisation in online debate: because people only perceive themselves as interacting with an inanimate machine and any response or feedback taking a certain amount of time to appear, rather than seeing a living, breathing human being reacting as they speak.
Help me out Slee as I am much like you. I pretty much avoid the echo-chamber of Fox News and Limbaugh but I haven’t been able to find an alternative to Drudge. I do realize his headlines and hyper-link descriptions offer more than they deliver though.