It's a good question, and one you shouldn't feel bad about asking. I've debated with myself on this matter countless times, and had the conversation with Amy and Ben a lot too, especially recently with them going fully vegan. I don't generally discuss this with anyone outside of family and my very best friends as it seems to have become as contentious a topic as politics and religion.
Basically, for me, I like meat. It tastes good and I feel it nourishes me. I also have no qualms about eating something that used to be alive. It doesn't bother me in the slightest. I am uncomfortable about unethically farmed meat, and I don't support factory-style farming, but personally I feel as long as I consume with a conscience, that's okay. I have a rather simplistic, perhaps naive view: all things die, why not eat them? If it weren't taboo to eat humans, for instance, I'd be fine with people eating me after my death. By that same logic, I am a donor. I have no problem with people taking my eyes and heart and whatnot once I'm dead - after all, I'll have no use for it. And by that same token, provided an animal has been well cared for and lived a good life, I have zero ethical dilemma about consuming it post-mortem. Humans have done so for centuries, and of course there is a large, loud argument now that we simply don't need to anymore, but regardless, we have done, we continue to do so and personally I'm happy to continue doing so. I don't have that thing where I think "cute little bunny rabbit, I could never eat you!" I genuinely do not see why if a rabbit dies I should bury it rather than eat it.
At its core, it is a primitive thing. A lion would have no qualms about eating me; likewise, I have no issue eating cow, and I'm sure if cows had predatory instincts they'd gobble me right up, too. I understand there are alternatives, I understand it's no longer necessary to my survival to eat meat; however, I like meat, so I continue to eat it. That said, I do so with a conscience - I buy free range meat and eggs, organic where possible. All supermarkets in New Zealand stock free range options, so they're not hard to come by, and a lot of the time there is literally zero price difference, which is why I'm astounded by people who continue to support cruel farming methods. If you can buy free range for the same price, why give your money to the wankers who factory farm pigs? Why not support Freedom Farms? I bought bacon last weekend and the Freedom Farms bacon was literally the exact same price, to the cent, as the factory farmed stuff. That I do not understand. Although, having said that, we eat at cheap restaurants occasionally where I can say with almost absolute certainty they do not use free range meat. So we're not perfect. But that's really no different to Amy and Ben being "vegan" but still drinking Bailey's at Christmas and driving a BMW station wagon with full leather interior.
There are so many arguments for veganism, and from a purely holistic standpoint I agree with it wholeheartedly, but at the same time I am an animal and I enjoy getting nourishment from other animals. I know this isn't morally sound and comes across as ignorant to people who have decided to take the higher ground and engage in no animal harm whatsoever, but truthfully, I'm not bothered by that. I'm comfortable with my lifestyle. I take what steps I can - I only eat free range (this includes with fast food; since moving to Auckland we almost exclusively buy Burgerfuel when we fancy a greasy treat, because they use strictly free range products only) and buy cruelty free products. To answer your original question, I do so because there is zero need to test cosmetics on animals. None whatsoever. And it comes back to that basic principle for me; while I choose to eat meat, I do so consciously, and where possible to avoid or reduce harm, I do so. Same goes for cosmetics. There is just no need for me to buy L'Oreal lipstick when I could get Lime Crime for the same price and know I've put my money to a more ethical organisation in the process.
As for veganism vs. vegetarianism; personally, I think going fully vegan is a really extreme step to take, and I too have seen people do so only to fail 12 or 18 months down the track. My good friend Tessa was vegan for two years and has recently gone back to being vegetarian, because of cakes. She was in a cafe one day and suddenly felt completely fed up with avoiding cake. She wanted a slice of chocolate cake, so she got it, and she's been firmly vegetarian since. She said sure, the vegan thing was good while it lasted, but ultimately she just does not see a huge problem with butter or honey, so she's eating them again. She still doesn't eat eggs, because she thinks the idea of eating a chicken's period is gross, but she's no longer hardcore vegan and said her mental state is so much clearer as a result. She feels calmer, freer and less stressed.
Amy and Ben are persisting with the vegan thing, but make concessions for treats like biscuits, cake and Baileys, which I think defeats the purpose altogether. If you're going to be so high and mighty as to say you are vehemently against even the idea of having pets, then you can't be like, "Oh, but biscuits are okay, because biscuits." Either you consume animal products or you don't, and by saying you don't but then changing the rules to suit your own taste buds is, I think, the most perfect example of human greed, and if anything simply proving the point they've been trying to disprove all along. It's like Julia at my work, who doesn't eat pork because they're "too much like humans", but is fine with eating other animals. That, to me, is the quintessential example of human superiority. "I won't eat pigs, because they are as intelligent as humans, but the other animals are dumb, so they're fine." Likewise, I disagree with vegetarians who avoid animals they feel they could form a bond with (cute lambs, cows, pigs, etc) but happily eat fish and seafood because they view them as emotionless.