A 30% national sales tax is a workable substitute for all income and payroll taxes in the United States.
Global warming is not primarily caused by human activity. In fact, global warming might not even exist.
Intelligent design is a viable scientific theory that ought to be taught in biology classes.
Even with marginal tax rates at current levels, reducing taxes will increase revenues.
Saddam Hussein was behind 9/11.
I came up with three examples, and also two marginal ones:
- Most genetically-modified organisms (GMOs) under most circumstances are dangerous to the environment and/or dangerous to human health.
- Bilingual education has better academic outcomes for English-as-second-language children than English language immersion.
- Animal testing and experimentation has very little medical or scientific value.
To expand a little, I said "most" GMOs because they can be dangerous in some circumstances. As for animal testing, Kevin didn't expect universal support, just a non-trivial cross-section, so I think it qualifies.
My two marginal ones: first, I'll bet it's more liberal scientists who doubt that the first peoples to reach the New World are responsible for the extinction of Ice-Age mammals. Second, liberals were probably more willing to apply post-modern theories to the sciences, although that's dying down and conservatives are starting to get worse.
Kevin's commenters had two more valid nominations: 9/11 was an inside job; and massive vote-stealing gave the 2000 and 2oo4 elections to Bush;
Marginal commenter ideas are that gun control laws have been proven effective at reducing gun violence; that the death penalty isn't a deterrent to murder; free trade hurts the middle class more than it helps; vaccines cause autism; and storing nuclear waste is a significant environmental risk (then I ran out of comment-reading steam). These are marginal for several reasons - in some cases they might not be completely disproven.
UPDATE: Based on the comments, I'll add "Subsidies for emerging technologies have been proven to generally pay for themselves." Glenn in the comments thinks the liberal's stronger enviro emphasis means they bear disparate responsibility for the myth that subsidizing corn ethanol is a good environmental practice, while I think the fact that so many conservatives espouse the same myth means it can't be blamed on liberals. Take your pick.