As it often goes, both extreme political views (liberal pro-science vs. conservative, ignore-science) have some good points to make, and some unjustified beliefs that harm mutual understanding. May I suggest that you do not try to challenge your father's views on scientists directly head-on. Give him an example of a scientist and a contribution that may be interesting on their own. It's much less likely that the refrain will be used to discard your effort. Perhaps tell him about a scientist who wasn't a liberal, perhaps had some similar views as your father has - but still believed in science. Tell him about Teller, who was as far from being a liberal as it goes, pushing for hardline foreign policy and bigger and better nuclear weapons. Still he was a brilliant scientist and he perceived the potential danger of climate change due to fossil fuels already in 50's. Tell him about Fleming, an army doctor who investigated sepsis, discovered pennicilin and helped bring the humanity a cure to many bacterial diseases.