It’s their Humanism that doesn’t allow them to see the dangers.
You can bring up Hitler, Stalin, Mao, etc, all day long, and it makes no impact on them, because they don’t even entertain the idea that the people in power now, that they support, could possibly do the things those guys did.
After all (and this is the basis of Humanism), “I’m a good person, so those I support must be good people too”.
well, THEY may be good people, but the persons they support may or may NOT be such good people
at the very least, they should realize that people attracted to powerful governmental posts could have either of at least 2 motivations,
1. to do all sorts of wonderful good things for/to society,
or
2. to mis-use the power for their own gain (and/or ego-maniacal ends)
If the “left” would at least acknowledge this possibility, that there COULD be a misuse of governmental power by certain politicians on occasion, then they would be more likely to screen their candidates to better achieve their true, goodygoody goals
I wish we could convince them of at least that much... we’d all be better off for the effort