Wormwood said:Why a 'bad thing'? It's not like they are going to outshine your specialists any time soon.
Well, I suppose I could come up with arguments myself, but I think Dave himself comes up with an awfully good argument against them:
And creating hybrid characters involves a careful balancing act. Multiclass characters can't be optimal at a focused task (because that horns in the turf for the single-class character) and they can't be weaksauce (because then you've sold the multiclass character a false bill of goods and he doesn't actually get to use the breadth of his abilities). There's a middle ground between "optimal" and "weaksauce" that I'll call "viable." But it's not exactly a wide spot of ground.
& is viable for your campaign going to be the same as viable for mine? If it's that tricky to get right, let's just skip it or err towards the "weaksauce" side. A viable gish isn't so fundamental to the game as to waste the effort on. IMHO, of course.