"I'm vegan, except for meat, because the meat industry already exists, so the cow is already dead. When the meat industry stops existing I'll stop eating meat. That's veganism."

Why would they want to contribute to something that comes from the already existing meat industry, and how do they justify consuming that being different than consuming meat itself?

If that person is supposedly vegan, that argument makes no sense. Lots of things would be acceptable for vegans if you just say ”oh, it's a byproduct of the already existing meat industry so it's OK”, including all dairy products.

Besides, the whole point is that there shouldn't be a meat industry at all, not finding excuses to fund it.

I don't think it really matters. For a vegan, following "the cow's already been killed for meat" can lead to some absurd outcomes. For a dietary non-ethical vegans it makes perfect sense. For an ethical vegan, it would not.

Nothing wrong with your shoes being plastic there are not really vegan alternatives that fit the bill most of the time.

Every single animal product is from an already dead animal (or one that will be killed soon by the industry in order for it to be profitable). Leather isn't special in this regard and you can say the same things about meat, milk, hair, bone, etc. Saying leather is a byproduct of the meat industry is itself a bit silly as the leather industry isn't just there due to people eating meat, it is an actually valuable commodity on its own and there are animals that are raised for their skin/leather and not their meat (e.g. snakes). It's all interconnected and there's no point to trying to read the tea leaves on exactly which animal products would count as "driving" the system and which would not.

I've known vegans that buy used leather products because they don't directly incentivize the industry. I personally don't gatekeep those vegans on that issue. But just straight-up going out of your way to get the animal product? That's not exactly a personal vegan choice lol.

Animal leather isn't really any better for the environment because the tanning process uses a ton of chemicals like chromium that are toxic, so if they decompose they leech chemicals into the soil, and the manufacturers tend to locate production in places like India, Bangladesh, Haiti, etc where they can get away with dumping huge amounts of chemical waste into the environment and can easily abuse workers due to low pay and lax health and safety regulations. And that's on top of the farm animals already contributing massive amounts to pollution and greenhouse gasses.

So unless their leather is artisanally handcrafted buffalo hide from a First Nations tribe that uses every part of the animal, they're delusional.