They’re both correct, it just depends what you want to say. 1. I don’t believe misinformation: I don’t believe lies I’m told. 2. Or, I don’t believe in misinformation: I don’t believe in the actual concept of misinforming people.

Definitely the second one. Use "believe in" when you're expressing faith, trust, or confidence in something, especially in concepts, people, or abstract ideas.

The correct sentence is:
"I don’t blame the people who believe misinformation." Why? * "Believe" (without "in") is used when referring to accepting something as true (e.g., "believe misinformation" = accept misinformation as true). * "Believe in" is used for having faith or trust in something (e.g., "believe in honesty" = trust in honesty's value). Since the sentence refers to people accepting misinformation as true, "believe" is the correct choice.

Both are grammatically correct but the meanings are different. #2 is a useless sentence. For a simpler example, consider these sentences: "Sally believes Harry." "Sally believes in Harry." The first means that Sally thinks that what Harry says is true. The second means that Sally has confidence in Harry. It is the difference between credence ("belief") and faith ("belief in"). All of us at least occasionally believe misinformation. Anything that is not true is misinformation, and all of us believe some things to be true that are false. If I believe the grocery store is located at 5 Main Street when it is actually located at 6 Main street, then I believe misinformation. Although your sentence #2 is correct, I would never say it. Information (and also misinformation) is not something that merits faith. It's either right or wrong. You either believe it or you don't. But you don't "believe in" it. It sounds totally weird to say you believe *in* the grocery store being located at 5 Main Street.

Both are correct. I can’t decide which sounds more natural. “Believe in” sounds a bit more theoretical or intangible (like “believe in god” or “believe in miracles”) whereas just “believe” is more straightforward and direct.