I dont remember the websites address, but i did once come upon a site that had quotes from gurbani that pretty directly asserted that eating the flesh of an animal is wrong. As for stories that the Guru's ate meat, im not really sure if they were true or merely rumors (personally, i dont think any of the guru's ever ate meat). I'm aware of the fact that some of the Guru's have killed animals before. The website I mentioned also addressed that issue. It stated that every animal the Guru killed wanted to be killed by Guru Ji (any of them)For example one of the stories (i think...) was about Guru Gobind Singh Ji killing a rabit. As soon as he killed it people asked him why he did such a cruel thing and he responded by saying that the rabit was formerly a person alive during the times of Guru Nanak and that he had done it a favor by passing him on to his next incarnation....
My point here is that there IS enough evidence in favor of sikhs not eating meat on religious grounds for us not to do it. This is probably why amrit dhari sikhs are instructed to not eat meat at all (they arnt allowed to eat meat even if it is non halal or non veal meat)