Why are some people in the Japanese self learning community so down on Heisig?

It's a book. Use it, don't use it. It's cool. If you use it and don't like it, that's fine. A lot of people have used it and didn't like it.

BUT a lot of people *have* used it and gotten a lot out of it.

It's fair to set out plusses and minuses regarding the book. There's a mix of both. Some people don't want to deal with the minuses, I get that. But the minuses that are a big deal to some people aren't a big deal to others.

In my case, RTK was a godsend at a time (2007) when there wasn't a really good way to study kanji. Now there are a variety of ways to do it. They all swap out a variety of plusses and minuses. None are "perfect."

For me, at that time, breaking the tasks down in RTK got me to come back to Japanese after a long break, because I couldn't find a method for learning kanji that worked for me. (I tried a crapton of methods, too... most were variants of "write this 100 times," and sucked for me.)

Are there ways more suited to a random person A or B? Maybe? I don't know. I'm not random person A or B, I'm only me, with my own luggage and experiences. So I can only go off of that. I found RTK to be reasonably effective if you put in the work.

Is it magic? Oh, hell no. It's not even a shortcut. If anything it's an act that requires delayed gratification and endurance, two things modern people have big problems with.

Other than that, it's just a way to separate tasks so you don't overload/burn out. If that doesn't work for random person A or B or C or D, then that's okay.

It's just a book. It's not going to bite. (Well, it might suck, but that's a personal opinion.)