Extremists like to use “alternative facts” or whatever other tactics achieve their goals. The means does not matter to them, only the ends, which they feel self-righteously justifies anything to achieve.

And then separately from that, gullible people also exist too. It is a bias that we all could fall prey to, though some of us seem more on guard against it than others.

(Tbf, many of those claiming those alternative facts are quite aware of just how nonfactual they actually are - they simply do not care as power, rather than correctness, is all that there is to them.)