It has nothing to do with being green.
The warnings are for pregnant women and children. These are safe for all others. Mercury is good for brain development, but in higher levels is dangerous for unborn babies, and small children. Just like alcohol. Technically it is good for you (ie. red wine and your heart) but it isn't recomended for pregnant women and children.
Research has shown that pregnant women and children do need a certain amount of mercury (in fish) for proper brain development, but large amounts of mercury (ie swordfish/shark) can be harmfull.
These stores are doing nothing "un-green" in selling these types of fish.



