How does your question make absolutely any sense at all?
The vegetarian/environmentalist does not eat beef...how is it confusing to you that he also does not believe it is good for the environment?
Or are you seriously proposing that "eating beef is good for the environment, since cows are bad?" Are you honestly that stupid? The more people eat beef, the more cows there will be. If no one wanted to eat beef, there would be no cows, and thus no environmental problems associated with them. Therefore, by not eating beef, vegetarians are reducing the demand for cows. This means there will be less cows and the environment will be better off.
How dense are you? Seriously.