I don't generally choose my reading list based on authors' political beliefs. I don't think that most readers do. Nor do I recommend that they should.
However, Stephen King isn't just another author who many people have heard of. He is a major celebrity, and a household name. He's been a celebrity and a household name for at least thirty years. Therefore, everything that Stephen King says or does is bound to attract attention.
And while his abilities as a novelist are well established, he often comes across as an uninformed but highly opinionated ideologue when he wades into politics:
Now King is using his money and clout in an attempt to sway a Maine Senate race.
Stephen King picks sides in Senate race
Stephen King--just like any other citizen--has a right to speak his mind on political issues in the public square. However, there is a point where it is not unreasonable to ask: Is King a novelist with leftwing political views, or is he a leftwing political activist who writes novels?