> No matter how bad harvesting of sea resources is, it can't be enough to abandon the oceans entirely

I probably don't understand your point (sorry english is not my first or second language).

At this moment we're seriously overfishing our oceans and killing it's population, that's what i have beef with (pun intended).

So your argument is - let's continue fishing?

> any more than the vast land-use impact of agriculture can be used as argument for abandoning agriculture

I'm arguing for changing agriculture (or better land management practices), not its abandonment.

I know you are! But if better land management practices is good enough on land, why can't better fisheries management be good enough at sea?

There are many issues, wikipedia seems ok, no time to summarize it, sorry.

[https://en.wikipedia.org/wiki/Fish_farming#Issues]

I didn't ask about what was wrong with fish farming.

I said: you don't want to cut out ALL agriculture, even though a big part of present agriculture may be unsustainable.

So why do you want to cut out ALL fishing and fish farming? I know the answer is that you're a vegan, but that doesn't cut it if you want to convince those who care about sustainability.