There is nothing morally wrong about doing something excusable. You can give examples, but they're all just the trolley problem with someone you care about (including yourself) on one branch of the track. Self-defense is not immoral; killing to survive is just dog eat dog,

Acts per se are neither moral nor immoral. Context is everything. Some immoral acts are forgivable, but that's not the same thing as excusable. Those cannibals in the lifeboat were convicted of murder and sentenced to death, but their sentences were commuted because what they did was forgivable and, arguably, they posed no threat to the public. (Queen v. Dudley and Stephens).

Don't vegans eat vegetables that are raised by forcing the animals who would eat them to starve, or worse? Would there not be more insects and rabbits if we didn't protect our crops from them? One winery I visited practices biodynamic production. No pesticides. Instead, they grow flowers that attract bugs that eat the bugs that attack grapevines. That does not sound like ethical treatment of the last-mentioned bugs.

Species displace their competitors, some by eating them, but others by eating what the competitors eat. Why are we somehow forbidden our place on the food chain? Homo sapiens is an invasive species. Suicide is the only way not to harm sentient beings in a way that allows you to use any of the products of human ingenuity, from agriculture to machinery. To pretend that veganism is morality is to play word games, nothing more.