Bad design, or awesome? Evidence for awesome: They can very precisely vaporize living creatures -- and their clothes! -- whilst leaving everything else (floors, walls, objects people are sitting on) untouched. Evidence for bad: Inconsistent power output. In Star Trek II, a phaser vaporizes a mind-controlling eel of Ceti Alpha V (also, the Starfleet officer it's inside of -- and his clothes!), but then turns another such eel into a smoky smear. Yes, one can dial down phaser power, but I'm pretty sure you can't actually set a phaser to "smudge."
You have your choice: Velouresque pajamas and miniskirts (resurrected for the 2009 reboot), burgundy jackets with puffy blouses (Treks II - VI), or progressively unflattering jumpsuits (Treks VII - X). Do Starfleet personnel ever stop what they're doing, look at each other, and ask, "Who dresses us?" They should. But all of the above are at least better than the eye-poking fashions of the first movie."