Shouldn't scientists be neutral? As a scientist this is an easy question for me to answer, but first let's be clear that "neutral" and "objective" are NOT the same thing, but are often conflated.
Science is all about observations, questioning, and improving humanity's knowledge. The answer to your question is obvious with empirical evidence. Most all "leftist" policies are objectively better for humanity than conservative policies. The examples are nearly limitless. Universal healthcare is cheaper and results in better health outcomes for every nation that has it. Public spending on public transporation is better for the environment (i.e. humans and the world we live in) and the economy than spending on private transporation. Etc. Etc. Without beating a dead horse, spending public funds on policies that provide services to the most people in a society is objectively the most efficient way to improve society. The opposite, consverative approach, so-called "Trickle Down economics" has never been shown to work for the majority of a country.
How liberal is always a question, but using the scientific method on thousands of years of human policy decisions, liberal policies are objectively better for any individual society, and humans as a group.
[edit]To finish my point (sorry, busy and distracted at work!) started at the top. We can see that so called “liberal” policies are nearly always objectively better for society as a whole. However, the very wealthy have always had a public voice proportional to their wealth, precisely because with their wealth they buy up media (and public figures including some religious leaders). So (for example) an average person might read 10 articles that factory farming is good for society, and 10 articles that say it is bad. A neutral response would say, “It is a toss-up.” An objective response would say that factory farming is bad for the environment, the workers in the factory farms, the health of people eating too much meat, and of course for the billions of animals raised in horrendous conditions who are slaughtered each year. An objective fiew is that factory farming results in great wealth for a few, at the expense of the many (both human and animal) and a better solution would be the elimination of factory farms and a more plant-based diet.
As a scientist, I was trained to not look at the politics of an issue (e.g. how many articles say factory farming is good or bad) but objectively at the empirical data (e.g. how high the toxic emissions and run-off are from factory farms, the high level of antibiotic resistant infections in those that work in or near the plants). Most scientists who stay working in science do the same, day in day out in our jobs. So it is logical that when we look at something like healthcare insurance, it is patently obvious that having the entire society paying into a single public system based on overall public health results is going to result in the lowest costs and the best results compared to a privatized system based on profit based results.
