I think the general consensus is that an unchecked Democratic congress would do far less damage then an unchecked Republican congress would. Dems generally question themselves and are generally more moderate as a group (See: Health care debate in 2009)....the GOP often gets unified and listens to the looney base way more often then it should.
Even so, a split in the GOP wouldn't guarentee unchecked congress for the Dems. The Tea Partiers would still vote in their Tea Party guys, and the "Moderate GOP", whatever the non-Tea Party GOP's would call their new Political party, would still win their fiscal conservative districts. And Republican states like Texas would still send Conservative candidates to the Senate...no way a Dem wins there even with a split vote. It's the presidency that a GOP split would make tough for a conservative to win.
I get what you're saying, and while I still thinking radical leftists are fundamentally incorrect I can at least appreciate the fact that the goals of collectivist policies are to help people. IMO, however, (and this is from a 3rd party viewpoint) the GOP and Democratic parties are fundamentally the same.