Crop agriculture kills animals too
It does, and that is a real cost worth taking seriously. It also counts against animal agriculture, which consumes far more crops than people eating plants directly.
Every plant-based meal still has animal deaths behind it: combine harvesters shred mice and ground-nesting birds, pesticides kill insects and the animals that eat them, and clearing land for crops wipes out whole wild populations. Veganism draws its moral line at whether an animal is killed for food, yet the animals killed to grow that food are just as dead and are rarely counted. If the aim is really to reduce animal deaths, then the diet that claims to avoid killing should be judged by every death it causes, not only the ones it can easily see.
Field deaths are real. Harvesting kills small mammals, birds and invertebrates; pesticides kill a great deal more; habitat conversion for cropland displaces wild populations. Anyone claiming a plant-based diet involves no animal death is overstating the case, and the point deserves acknowledgement rather than deflection.
The difficulty is that it does not favour the conclusion it is offered for. Farmed animals are fed crops, and they consume several times more calories than they yield. A diet routed through livestock therefore requires more cropland, and more harvesting, than one that is not. Estimates of the exact ratio vary by species and system, but the direction is consistent. If field deaths matter, they count against the option that requires more fields.
Rejecting a claim by pointing to inconsistency in the person making it. Hypocrisy may be worth noting about the person, but it has no bearing on whether what they said is true.
How it applies here: Points to inconsistency in the vegan rather than engaging with whether the harm should be reduced. Even if the inconsistency were real, the question of which option causes less harm is untouched.
Rejecting a workable option because it falls short of a perfect one. Also called the perfect solution fallacy. The relevant comparison is with the realistic alternative, not with perfection.
How it applies here: Treats any remaining harm as grounds for abandoning a reduction in it, rather than comparing the two available options against each other.