I say this as a member of a leftwing party in my own country which could use a little more thinking and building politics up from principles and a lot less blind parroting of what the tribe’s chiefs say.
(We also have a Communist Party around here and those are even worse).
There is quite a large overlap between leftwing and the highly educated (maybe even intellectuals) so leftwingers are thinkers rather than flag waving parrots much more often than rightwingers. However, humans being humans, even many of those can get a strong emotional bond with a party, by which point they become unchallenging and unskeptical tribalists.