The truth is that the amount of fish we extract from the ocean every year is incredibly damaging not just to the oceans, but to everything. The oceans are the largest carbon sink by far, and fish play a key part in moving organic carbon captured on the surface deep in to the ocean where it can be sequestered. It's been estimated that for every $1 we pay to buy fish we're doing about $10 in long term damage from global warming.

So, why don't people change? Because no one person doing something different will affect the world, and people would rather keep doing something they enjoy, but isn't sustainable. The other option is to give up something you enjoy just because it's the "right thing" even though most other people won't.

A similar argument can be made for eating meat, animal agriculture is one of the largest forces damaging the environment in just about every way, including global warming. But we don't see any big movements to abandon meat, or invest in lab grown meat or other alternatives.

The documentary Conspiracy does a great job of looking at why even big environmental charities ignore the huge impact that changing diets could have on the environment.