I think this is the wrong take. A discerning reader can read all manner of crap and know its crap. It can even learn how to avoid doing the same styles of mistakes in the future by reading it. So it affects you, but in unpredictable ways. Not like you're trying to say like "read bad things -> become bad".
To give you a specific example (lets not call it crap this time). I've read more communist literature than I can list right now and I'm a social democrat and think Marx is full of flaws and communism is a hugely flawed economic system.
You are shaped by what you read, but not in the basic "you'll agree with what you read".
That's not my argument and I don't think it's the article's argument either. "You are what you read" doesn't mean you agree with what you read any more than "you are what you eat" means you'll turn into a potato chip.
My point is more like, do you want to devote a bunch of your thinking time to arguments about communism or politics in general? Maybe you do and that's great, but I very much don't. I've thought about politics plenty in the past and formed my opinions already. I'm not a politician and don't care to evangelize my political beliefs. I have very limited time these days and I want to spend that time thinking about other things. Things that matter to me.
I follow people who post useful and interesting things on those topics. However, those people also frequently discuss politics. And although I know those posts aren't why I follow those people, seeing them constantly makes them impossible to ignore. I end up spending time thinking about stuff I know I don't want to spend time on, even later when I'm not reading it. So I mute the words "liberal", "conservative", and a whole lot of others. Now I can follow those people but still spend my time thinking about the things that matter to me instead of politics. And over time, that literally changes my brain.
To give you a specific example (lets not call it crap this time). I've read more communist literature than I can list right now and I'm a social democrat and think Marx is full of flaws and communism is a hugely flawed economic system.
You are shaped by what you read, but not in the basic "you'll agree with what you read".