When extreme moral philosophies try to exist in a complex economy, allowances have to be made for human limitations.

Abolitionists couldn't exist entirely without the products of slavery and anarchists can't exist independent of the state, but that doesn't change the point of what they're trying to do.

Undisciplined

That's a more accurate word, still feels odd to me that the rules are open to so much interpretation

culture

Why are vegans ok with using plastic products?

You're right. The real definition uses the word "practicable", which is obviously weaker.
> Veganism is a philosophy and way of living which seeks to exclude—as far as is possible and practicable—all forms of exploitation of, and cruelty to, animals

Like most ethical systems, there's an acknowledgement that living requires being able to act without fully accounting for the morality of each action.