I'm a fishbelly-pale white dude living in the American West. One of my major concerns is sunburn and I detest slathering greasy sunblock on myself so I have come to almost always wear pants. Better brush/bug protection, too. In hot weather I find that I like RailRiders EcoMesh pants- they vent very well so no problems with overheating. (And their EcoMesh, Equator, or Madison River vented shirts.) Bonus- you can get them pretreated with Permethrin- they call it "InsectShield(tm). IMHO, RailRiders "gets it right" in the trade off between weight and durability. Even their "heavier" Weatherpants are pretty light.
There's a reason that throughout the middle-east people have always worn full-sized flowing robes- to protect them from the sun. The sun beating on your exposed body is much more of a threat than some sort of theoretical overheating from wearing lightly-colored loose clothes that cover you adequately. I suppose in the American Southeast where the humidity is absurd one might think differently, but even then I'm not so sure.
Weight isn't really an issue- you can find some incredibly light pants. I think that the extra protection is easily worth a couple or three more ounces.
But I do occasionally wear shorts on quick dayhikes, and on the occasions were I trail-run.
I've come to not believe in convertibles- they are heavier than plain pants and the zippers are two more things to fail, then you're stuck with shorts, anyway. (And all of the ones I've used have been incredibly over-built, again adding to the weight, while simultaneously using flimsy zippers for the convertible legs.) Granted the EcoMesh pants have two extra zippers, too, but if one fails the leg doesn't fall off...
Just commit, and pick either pants or shorts. And, actually, it isn't insane to bring both and wear a set of running shorts with a liner as your underwear under the pants, and just take the pants off if you feel the need- especially if you can find some insanely light pants like the old BPL Thorofare pants. GoLite makes some decent shorts (or they did the last time I looked) that can be worn as underwear.