If the muslim, altruist, and monagamist from your example knowingly continue a behavior that is antithetical to the definitions of their stated identities then

If the muslim, altruist, and monagamist from your example knowingly continue a behavior that is antithetical to the definitions of their stated identities then they are not a muslim, altruist, and monagamist. They may like to be or strive to be, and they can change, but they aren't right now. They should be excluded from the definitions. You're right in identifying pet food and unknown ingredients as grey areas. "Practical and practicable" provides a tremendous amount of grey area. However, knowingly consuming animal products when there's an alternative is not a grey area. It is antithetical to veganism. 99% vegan is 99% better than the alternative, and that's undeniably great. I'm pursuing this so that people reading our conversation are not confused about what veganism is.