A couple added thoughts. Every feeling you get as a result of virtuously carrying out your duties to family, community, and all that other lovely stuff has some neurological base. So presumably, it's in principle possible to replicate those subjective feelings through technology. That doesn't mean I'd necessarily want to do it—the point of Nozick's famous experience machine thought experiment was that we care about more than happiness, even in the most exalted, non-hedonistic conception of the term. We're satisfied when we achieve our goals, but often what we're really aiming at is precisely the achievement of the goal, and not the satisfaction.
That said, I'm probably more inclined than most to attribute much of our day happiness or unhappiness (I'm not talking about anything as serious as clinical depression here) to chemical blips than to the deep, subconscious psychological roots many seem to assume must underly those moods. And the two aren't disconnected. If you wake up feeling grumpy and lethargic, how effectively are you going to fulfill your goals? And when you wake up feeling refreshed and optimistic, maybe for no particular reason—aren't you more apt to be a better neighbor, friend, lover, worker, student? We're already largely subject to these sorts of chemical flukes—is it somehow worse to be subject to the same chemistry under our own control?
The fear animating people who worry about this aspect of biotech seems to be the "soma scenario"—that happy pills will somehow subvert or replace the more familiar "pursuit of happiness" (or eudaimonia, or whatever). They seem more likely to supplement it.