The people saying that one needs to eat meat to be an elite athlete are simply wrong. As someone has already pointed out, there are so many supplements these days that give you everything that meat would deliver, minus the moral quandary. Between a sensible plant-based diet and supplements, you're literally not missing out on anything aside from the deliciousness of meat.
I personally eat whatever. I try to keep it mostly healthy though. (If only they could make a 0 calorie beer... or maybe I should just start dosing myself with GHB? lol) I've had many vegetarian / vegan friends and when it comes to sustenance, I really like convenience. Being a vegan is a huge pain in the ass.
I personally find factory farms disgusting and morally wrong, and I can't even bear to watch a video of what goes on in there, but realistically speaking, it's difficult and expensive to find ethically grown and slaughtered meat products in many areas. (Some would argue that there's no such thing as ethical meat products...) I could easily be a vegetarian or a vegan if someone prepared all of my meals for me and did my shopping, but when I'm driving around stoned, I'm not thinking of ethics when I pull into a Taco Bell and order a burrito.
I see nothing morally wrong with eating fish / seafood... plus, fish is one of my favorite foods and I couldn't see myself not eating 'em. Here in Missouri a lot of people have man-made ponds on their property that they stock with fish, which I think is a great idea. We need more private stocks and fish farms in general. People should really lay off the beef because of the environmental factors involved. Beef production is hell on the environment. Look at what is happening to the rainforests in South America... if we lose those rainforests, the whole planet is f@#!ed. Pork production is pretty bad (and disgusting) but the environmental impact is nowhere close to that of beef production.