I was a (non-proselytizing) vegetarian for ten years, and one of the reasons I stopped was I saw the futility of the whole pursuit-of-absolute-purity thing. At the time I was working on an organic farm, and knowing that most organic farms fertilize with manure, blood meal, and bone meal – much of it by-products of the meat industry – made the whole thing much more complicated in my mind. Keep in mind also for you dairy eaters that something is happening to the half of each generation of dairy animals that are born male, and it’s generally not “run around in pastures and die of old age.”
But whether it’s a result of mellowing with age, or just getting some distance from new-convert zeal, I find that most of my long-time vegetarian friends no longer get on their high (tofu) horses about how few animals their lifestyle kills versus mine. There are always exceptions, but I find that most mature people are not that interested in what others eat. Or have grown the sensitivity to keep quiet about it. It’s easy to characterize all vegetarians as ridiculous by pointing to the extreme examples, but it’s like trying to characterize everyone who’s Christian by pointing to Jimmy Swaggart and saying, “Look how silly.”
As far as the OP goes, if you refuse to throw garbage out of your car window, you can’t expect to notice any difference on your local highways in a week or a year. I wouldn’t take that as a sign that it’s pefectly fine to throw trash out your car window. Or that by not devoting your life to keeping other people from doing so, you’re somehow being hypocrticial and not doing enough to fix a problem. You could play this game with just about any moral decision you choose to make: you’re polluting by driving a car, you’re still contibuting to pollution by taking the bus, an electric car is still made by a plant that pollutes, the highway infrastructure causes toxic runoff and destroys habitat, x number of people die every year maintaining the electrical grid, etc. In my mind, tempting through it may be, you can’t view this stuff in the Manichaean world of sin or purity and nothing in between. It’s all gray, and you do what you can.
When it comes to woodchucks under the combine, it’s hard for me to see what the option would be, besides starving to death, or an extreme Jainistlife style where you’re only eating fruit that’s fallen off trees and wearing a veil so you don’t breathe in any bugs by accident. Believe me, subsistence farmers defend their crops against animals with whatever weapons they can get their hands on.
I don’t eat meat every day, and I try to buy organic meat and free-range chicken when I can get it. Ten years ago it was hard to find; now just about every supermarket I go into has chicken raised without antibiotics, eggs from free-range hens, and some kind of non-feedlot meat. So your individual choices can change how agriculture is produced, even if it takes years.