When being a vegetarian became too main stream the crazy “look at me” type vegetarian crowd went vegan. It was no longer chic just to be a vegetarian.
A diet that is too heavy on meat and carbohydrates like some American diets is also bad for health - without the fibre, one is at higher risk from cancer and constipation (starting with the cs :) among other issues
the correct diet is in-between: eat a lot of veggies, but also some meat, fish, eggs, etc. Even red meat is perfectly fine in moderation (depending on your genes that can be once a week or more) and fat is good, again, in moderation.
Probably the only really bad thing to avoid (with no redeeming quality) is refined sugar. Zero value.
And refined white sugar is everywhere - even down to bread etc.