Plasma produces far more collateral damage (potentially to the user) with far less utility. - Edit 1
Before modification by Joel at 27/09/2012 11:47:06 PM
xkcd claims they can start fires and burn skin. There are a couple videos at the sales site, one of the laser popping a line of 100 balloons and another of it popping corn (though the latter required two lasers and 60 seconds.) Still, even if you cannot draw your 1 lb. laser (at least this one) from your hip holster and put a hole THROUGH someone, you can burn the crap out of them and/or ignite their clothes so they go up like a human torch. 
What? Why are you all looking at me like that? These are LASERS! They are COOL! Er, HOT! SCIENCE RULES111 (BILL, BILL, BILL, BILL....)
What? Why are you all looking at me like that? These are LASERS! They are COOL! Er, HOT! SCIENCE RULES111 (BILL, BILL, BILL, BILL....)Even Lucas, flannel-wearing, violence-dislike hippy-type that he is, made laser blasts, as opposed to beams. Bolts, bursts, blasts, bullets - these are the properly phallic projectile products of manly weapons. Star Trek phasers stunned or vaporized, so they could get away with beams (some versions looked more like remote controls than proper guns) and that was some sixties-future-utopia that looks to have been somewhat neutered anyway.
For that visceral satisfaction, you need destruction with a single trigger pull, not a continuous beam. That latter is how Protoss weapons work. Terran stuff just blasts out in shots or bursts.
Star Trek actually had a plasma TORPEDO, though they did not call it that at the time: The Romulan weapon in "Balance of Terror." It was an absurdly powerful weapon almost on par with the Death Star; you may recall it severely damaged a star base buried many miles below the surface of an asteroid—and a second blast ATOMIZED THE ASTEROID!
Star Fleet Battles and Cosmic Balance both later defined it with technical specs; I never played the former, but played the latter a lot. I remember the plasma torp well: Unlike phasers, it lasted for three turns after it was fired, tracked targets and badly wrecked their shields; it also had a nasty habit of wrecking whoever fired it if they 1) made the mistake of firing it in the direction they were traveling at high (or even moderate) speed or 2) passed between it and the target before it dissipated.
Plasma is not your friend: It is a clumsy erratic weapon therefore nearly as dangerous to the wielder as to the target. Exhibit B is the only plasma we actually DO use as a weapon: The fusion bomb (though the fission-fusion version is not nearly as dangerous as, if less powerful than, the fission-fusion-fission variety.)
Lasers, however, can be precisely targeted to avoid all surrounding objects, and deliver virtually all firepower undiminished by range except at significant distances. They are more akin to rail guns in that respect: As long as nothing gets in the way, anything you point them at will be almost instantly annihilated (if something DOES get in the way it will be annihilated instead, but that is only possible for a split second between the time you fire and the time your target is destroyed.) Calling these lasers "lightsabers" is a bit over the top (and ignores their behavior,) but in the sense that they are "more elegant" (i.e. precisely targeted,) the comparison is valid.