Rationalwiki is extremely left biased. They admit their biases when you look at their main page, but they didn't have the guts to call themselves progressivewiki.
You have misrepresented what Rationalwiki considers themselves. It was started by Conservatives who did not agree with the extremely anti-science of the Conservapedia. It is broader than just conservatives now, but calling it an "extremely left biased" source is just silly. More importantly, they have not admitted it.
They take an extremely pro-science, and anti-conspiracy theory position. If that makes them "left biased" these days, that is a statement on how far out the Alt Right has taken conservatives.