I don't agree with your second point about 'smear claims.'
Certain people do have an agenda to make it look like there is not a consensus on a scientific theory when there really is-- oil corporations say that there are plenty of credible scientists who don't believe in man-influenced global climate change, and creationists say that there are credible scientists (mostly pediatricians, probably) who don't believe in natural selection.
Now, I would be willing to acknowledge that smear claims largely politicize science, which is something which should be free of political influence, but the issue arises in that the converse is not necessarily true- you and I probably agree that politics should be influenced by science. For example, a homosexual cannot "turn" straight through therapy and prayer, so, scientifically, it is logical to support equal rights for homosexuals. More broadly, scientists (climatologists in particular) do tend to agree that the reason for global warming is the influence of man, so it would be reasonable to implement policies to attempt to repair the damage done by man in the last hundred years.
Naturally, if we allow science to influence politics, it is inevitable that politics will influence science, if we aren't careful.
That being said, there are some issues where I am willing to disagree with the scientific consensus. For example, I largely feel that the reason so many countries are enacting smoking bans is because of influence by pharmaceutical companies, who use anti-smoking efforts as a way of increasing sales for nicotine patches and gum. I'm not sure who profits off of the idea that global warming will kill us all (maybe hybrid car manufacturers), but it's obvious who profits off the idea that it won't.
Science cannot influence politics because it doesn't take normative stands. It does for instance not follow from the fact that homosexuality is genetically determined that gays should have equal rights. It also does not follow from the fact that global warming is man-made that we should implement policies to amend it. You would have to introduce ideas about equal rights or the welfare of humanity that have nothing to do with science in order to reach those conclusions. The idea that ideological view-points should be based on and are legitimized by scientific findings is generally quite dangerous.
