Philosophers are known for disagreeing with each other a lot, sometimes in a way that gives people the impression that the whole pursuit is fruitless. Of course, the view that philosophy contains some irreconcilable disagreements is itself a philosophical position. Even if you don't like philosophy, you aren't able to avoid taking philosophical stances.
One reason people think philosophy is a trivial enterprise is that it is perceived that all philosophers do is argue about the meaning of words. And many famous disagreements are of just this sort! Scanlon and Parfit argue about the correct definition of the word "rational," and Judith Jarvis Thomson has argued vehemently that there is no subjective sense of the word "ought." Some race theorists argue that, properly understood, minority racial groups cannot truly be "racist."
However, if you think that these are the only kinds things philosophers disagree about, you are wrong.
When I make the claim, "You ought to be vegan," you and I can agree upon the same definitions of those words and still disagree on the truth value of the statement. This indicates fundamental moral disagreement.
Conversely I might also say "It is rational [Scanlon's sense] to be vegan" or "It is not rational [Parfit's sense] to be vegan," and both of these statements could be true (this is not, in fact, where their disagreement about rationality lies). Once everyone in the discussion understands the way the words are being used, disagreement disappears.
What Scanlon, Parfit, Thomson, and others are doing when they disagree about the meanings of these words is a bit complicated. I think in general, they are trying to say that the most natural reading of the word fits their definition. They will all admit that if you stipulate that the word carries a certain meaning in a particular context, then it can mean whatever you like. However, they also have normative views about how we ought to think and behave, and they think that the fact that a normatively loaded word (rational, ought, racist) has their particular natural reading gives credence to their substantive view.
Some people find this kind of disagreement tedious and futile. At times, I am tempted to agree. If you are insistent enough that a word means something, I might agree, but the relationship between a word and its definition is essentially trivial. If I say "Murdering people is always wrong," but by "murder" I mean "wrongfully kill," then I've essentially said "Wrongfully killing people is always wrong." Which is true, but quite uninteresting.
When I tell you that I believe that we ought to avoid the unnecessary suffering and death of animals, I expect that you'll agree. I hope that a further understanding of this principle and the world will get you to go vegan. However, I am not relying on the mere fact that we have definitions in common to motivate you. Rather, it is the truth of the fact that unnecessary suffering and death is bad that is compelling.