"Why bother going vegan at all when you can't go 100% vegan (see: meatless mondays), you're still going to hurt animals by supporting unethical businesses"
There is a growing contingency within the vegan community that seeks to eliminate these businesses - Here is an explanation and a link to a resource list. There are in principle two stances you can take on this issue: either plant-based capitalism is unacceptable because you're benefiting organizations that have hurt animals for them having done so, or on the other hand you might believe that because you're expanding the grocery isles and hopefully capturing more would-be vegans, it's acceptable losses (I personally haven't seen anyone present any hard numbers that would convince me that the latter scenario is ever actualized though). Either way, this is an argument for more veganism, not less.
If you do in fact think that more vegans are of the latter type and you have some hard numbers, I'd love to hear them, but most of these arguments seem speculative at best. Articles by vegans promoting PBC don't seem to actually talk much in the way of X companies, Y dollars, Z animals, so it just isn't clear that we're out of the realm of some minor accidental collateral that just exists as a part of being alive that you have no real choice in if you want to be alive.
Let's say someone held your family hostage and made you kill a rabbit with a sharp rock to let them go. Does it then follow logically that you should go out and eat meat following this episode because now that you've killed the rabbit you can no longer be a "perfect" vegan because of what you did when you had no choice? If you have a choice, make it against animal murder; if you have no choice then you don't. If your argument is something that you do that may have some minor potential knock-on effect that isn't clear, then you're probably here.