One of the most common talking points that I hear from people who are advocates of leather, especially those who work within fashion, is that leather is simply a byproduct of the meat industry. The claim that it is simply a by-product of the animal agriculture industry is used as their justification to buy leather products because they think that they're just the waste of the meat industry and that they are up-cycling material that would otherwise be thrown away. What these proponents of leather never address though is that these so called "by-products" are just another way in which the meat industry profits and that leather would not exist in the first place if it weren't for the raising and butchering of animals! Like I am genuinely baffled that people believe that the meat industry doesn't proliferate its existence through the selling of things like animal skin and the other remains that aren't flesh. Of course this doesn't even touch on the environmental impact required to produce leather, which includes that of the meat industry that raises the animals (which has a horrific impact already) plus the additional awful production practices like chrome tanning that are extremely common in the leather making process.
Also, a thing that especially irritates me in the TikTok video that I linked is the creator equating faux leather with plastic leather or pleather, when faux leather encompasses more than just pleather and contains leather alternatives that aren't made from plastic! That seems like something you should know as someone whose job requires a large knowledge of textiles/materials but I guess he for whatever reason doesn't know that or at least doesn't mention it