We have to stop expecting that some magical chemical is going to do the homework for us! leave poor fish alone swimming in the seas. Of course omega 3 dealers will claim that it keeps you happy, that it grants you eternal life and stuff and that superman endorses it...
The task at hand is to learn to live peaceful happy lives by ourselves, with the power of our minds alone without resorting to external stuff.
Our minds are often what put us in these situations to begin with, relying solely on them won't work for everyone. However, I see what you mean and, even if they don't actually do anything, then a placebo that can offer a shred of confidence or keep us going a little longer won't do us any harm. (Note: I'm not saying fish oil is ineffective, I'm speaking in general terms.)