Actually, I know you don't. The complexity involved exceeds the intellectual ability of a single person, no matter how arrogant they are.
Because you, single person, do not have the ability to ingest all the data, do not have access to the necessary supercomputers, do not have the decades of time to write and adapt the simulation software, do not have the PhDs.
You are simply one brain. Who very most certainly does not have the accuracy of the current models (yours is FAR less reliable, because it is your lone opinion), you think you have everything nailed down to brazenly assert "it won't be that bad", and well, you are just one dumb internet person, so I KNOW you don't know enough to back up your opinion.
If you followed the simulations alone, you'd see that they have had a surprisingly good track, even the late-1990s models are doing disturbingly well (which were more pessimistic than what the climate scientists wanted to say back then).
Ocean acidification and the potential collapse of oceanic phytoplankton should scare the living shit out of you. Fishery health aren't really the concern if oxygen production from phytoplankton drops. The inability to eat sushi is far down the list from "inability to breathe". Hint: phytoplankton produce 70% of the oxygen we breathe, and our society is actively participating in Russian Roulette on a global scale to see if we kill ourselves with that, among other "fun games" that "you aren't concerned about".