I pretty much only want happiness - for me, my family and, ideally, for everyone else. I do think, though, that with that also has to come having the right priorities and being able to appreciate all the different types of happiness there are (whether they're small things or sources of happiness that are "deeper").
People who are "generally happy" have clear enough heads to be able to think about people/things beyond just themselves. I don't particularly believe that one needs sadness to be able to appreciate happiness or to learn. Much learning can happen by listening to other people (REALLY listening) who have learned from one or another kind of sadness/"non-happiness"). People who are mostly happy and have little experience with sadness do have to watch out for "the arrogance of happiness" (also often associated with "arrogance of youth", which essentially means not having lived long enough to have run into enough bad experiences; or else living a relatively charmed life that allows one to hang onto his youthful arrogance well beyond what is ideal).
The matter of youth and arrogance, however, are separate from whether or not one has to have sadness in order to know and/or appreciate true happiness (or all the different types of happiness).
Assuming someone has outgrown (or been taught to know better by adequately skilled parents) any arrogance of youth, being happy helps fortify people so they have plenty of "emotional strength" for dealing with the sadder things in life. Having many sad things in one's life just gives a person a lot of practice at coping (but coping skills can be learned by listening to others who have good ones).
I'm sorry... Sadness (and sometimes horror) stinks. The less of it, the better; and let's not allow ourselves to spin it any other way. Can we figure a way to get something positive, or dig up some positive, out of sadness? Yes, but again, those are usually things we could have gotten some other way without the sadness.
Maybe many people think we can only learn about happiness from the bad stuff because they were too arrogant to listen/pay attention to others before a bad thing happened to them. Maybe some say that just as a way to "put a shine on a sneaker". In any case, the right kinds of happy (and there are more than one) are better, and I don't think there's much anyone learns from sadness that they couldn't have learned some other way if they were paying attention to someone other than themself).