If I'm following, your reasoning is that because (a) it's effectively impossible to live in the modern world without benefiting from the deaths of animals that (b) any attempt to limit the number of animals we kill to support our daily lives, or the kind of animals, or how they lived or died, must be pointless.
I find that jump from (a) to (b) is unfounded. There's a qualitative difference between (i) a mouse killed accidentally by a combine, (ii) a lab rat killed by a drug company, (iii) a pig raised and killed to be eaten, (iv) a mink killed for its fur and (v) an endangered mountain gorilla killed so a collector can stuff its head and hands. Different people draw their moral lines at different places.
A lot of people might have a problem with (v) but be okay with (i) through (iv). I can personally live with (i) and (ii), but have a problem with (iii) especially given the messed up fact that while almost a billion people on the planet are malnourished, the US has enough excess to give the majority of its soy and corn crops over to feeding livestock. As in, we're literally choosing to feed the pigs, cows and chickens we're going to kill before we feed the poor. I know of people who will accept (ii) if the research is for a compelling medical cause, but not if it's for something like cosmetics. I know plenty of people who can live with leather, but won't accept fur based on the crazy cruel stuff that happens on fur farms.
This stuff isn't black and white. You can't just equate animals that died millions of years ago that turned into oil with animals that we raise to kill; not all animal deaths are equal. The ethical and moral questions get complicated, and there's a lot of grey areas encountered when balancing human needs and desires against the potential suffering of creatures whose subjective experience we can't understand. And then there are health arguments and environmental arguments, and it never ends. Given that it's complicated, please have a little respect.
You write as though you expect that vegetarians and vegans must not be aware of natural predators or animals killed unintentionally by humans for reasons other than meat, or the weird, myriad ways we use highly processed animal products in the modern world -- and that if we had been aware we should obviously have come to the same conclusions you did. That presumption, that vegetarians and vegans must have made their life decisions out of simple ignorance of the facts, is a bit offensive. I'm not saying you should believe anything different about eating meat. But please don't flippantly talk down to people who have chosen to draw their moral distinctions in different places than yours.