Can "show-stopper" have a negative connotation?
Solution 1:
http://en.wikipedia.org/wiki/Showstopper
Show-Stopper in the theatrical sense is an expression referring to something truly dazzling. "The triple somersault in the dance that starts the second act is a show stopper"
The show has to stop for applause... it can't keep going if the crowd is on its feet cheering.
Of course you're correct that show stopper in the world of technology and business is an impediment to progress which must be cleared to proceed, and in that sense is entirely negative.