First, let me state that there are just as many anti-science democrats as there are anti-science republicans. For every creationist, there is an anti-vaxer. For every anti-climate change lunatic, there is an anti-nuclear fool.
But that's the individuals. They don't matter. Their are lunatics in all social groups. The problem is the Party Leadership and the political platform.
The left does not carve their anti-science message into stone as core party beliefs. The left doesn't have major candidates endorsing the anti-science views. It doesn't have litmus tests for candidates, demanding they repeat a viewpoint that is patently false. The democrat presidential party candidates avoid those issues, as opposed to bring them up.
That is not a minor difference. It is a major difference between lip-service for bullcrap and actual laws. More importantly, by not promoting it, we enable our own growth. In 10 years, the anti-vax movement will have to be taught in history schools because it won't exist anymore. Some day, with a bit more advancement, we can make nuclear power safe enough that even the paranoid masses will accept it (it is already far safer than coal.).
That can't happen to the GOP. Their anti-science movements have gotten stronger and stronger, and have stood the test of time. Evolution is proven science, it hasn't been controversial for 50 years, but the GOP keeps promoting Creationism. The same goes for Climate Change. In fact it has gotten so bad that moronic politicians point to the left's pro-climate change stance as proof we are anti-science. Climate change is accepted science, not something you can dismiss and claim is controversial (not among scientists at least).
That is why the GOP gets the anti-science rap. Not because liberals are more scientific than conservatives, but because the Republican party embraces anti-science movements while the Democrats are ashamed of them.