There's absolutely no reason everyone's threat model has to equate insiders with outsiders. If a stranger on the street gives you candy, you'll probably check it twice or toss it away out of caution. If a friend or family member does the same thing, you'll probably trust them and eat it. Obviously at the end of the day, your concern is the same: you not getting poisoned. That doesn't mean you can (or should...) treat your loved ones like they're strangers. It's outright insane for most people to live in that manner.
Same thing applies to other things in life, including computers. Most people have some root of trust, and that usually includes their vendors. There's no reason they have to trust you and (say) Microsoft employees/Apple employees/Linux maintainers equally. Most people, in fact, should not do so. (And this should not be a controversial position...)
