Why do celebrity chefs like Gordan Ramsay and Anthony Bourdain dislike vegetarians & vegetarianism and diss them so much?
Because it severely limits your eating options. To use another example, if you told those same chefs you only eat meat, you would get the same reaction.
To a chef (and the millions of foodies in the world), dining is much more than simply re-fueling your body. There are so many ways to craft unique dishes that please the palate.
To a chef, limiting your diet, eliminates so many possibilities to enjoy the experience of sampling all the great dishes crafted by chefs (and home cooks).