Probably too many reasons to list, but here's my partial explanation:
Senator McConnell stating the GOP's main goal is to make Obama a one term president. Parroted by Michele Bachman and others.
Abuse of filibusters and congressional rules to obstruct legislation.
Refusal to pass legislation once advocated by the GOP, if Democrats also agree.
Too many Republicans having taken an oath to serve Grover Norquist instead of serving their constituents.
The ridiculous vetting of candidates that begins with religion, where only Christian conservatives make the grade.
Dominance of religion and social conservatism over any type of actual governance.
Anti-federal stimulus unless it means paying (their) state debts with federal monies.
Proclaiming the way to growth is to cut all taxes.
Involving our nation in two Wars of 'questionable merit', while cutting taxes.
Inability to admit when policy was wrong, and refusing to take responsibility for their part.
Idolizing Ronald Reagan as a conservative while denying his role as a moderate.
Suggesting only Republicans are freedom loving patriots, and all Democrats are SSSocialists.