You can't be 100% vegan, so why
The original philosophy doesn't state we have to be 100%. This is a straw man argument.
It states -
[…] 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 for food, clothing or any other purpose; and by extension, promotes the development and use of animal-free alternatives for the benefit of humans, animals and the environment. In dietary terms it denotes the practice of dispensing with all products derived wholly or partly from animals.
It makes a lot of sense. Its about doing our best.