Most people "avoid slaughterhouses" in the same way that most people "avoid vegetable canneries". Which is to say that people don't visit these sort of facilities because most people don't have any business to do at one, nor do they think that visiting a food processing plant is a worthwhile use of their time.
Incidentally, I used to work in a bean canning plant. No random members of the public ever visited us.
The point is that people don't visit food processing plants regardless of what kind of food is being processed, not because they're scared of canned beans or seeing where meat comes from.
And certainly not because the plant is hard to get to, where did you even pull that from? The processing plant I worked at didn't even have walls, the whole building was a pavilion. Anybody could have walked in if they wanted to, but nobody ever did.
Incidentally, I used to work in a bean canning plant. No random members of the public ever visited us.