Trust me. If bowfishing for any species of gar was the sole reason that a population was dying out, it would be outlawed. Every state has an agency that spends hours deciding regulations for sportfishing and hunting. There are several commissions and even the federal fish and wildlife service which monitors these things. If something is legal, it won't drive a native population to extinction anymore.
If you want to talk about death, yes bowfishing is lethal almost 100% of the time, but the hook and line release mortality of several other species of sportfish is very high. Just because you let it go and saw it swim away, doesn't mean it survived. Many fish are so exhausted from a fight that once they're released, they die shortly after. I don't have exact numbers, I don't have the time right now to get citations and do more extensive research, but release mortality of sportfish is a little talked about problem that is bigger than you think. It's why there is a huge push toward using circle hooks for many species.
If you want to attempt catch and release, hook and line is the best way. If you want to catch and consume, bowfishing is a fun and legal way to do that as well. Just because you don't like to do it, doesn't make it wrong or anyone on here stupid.