First of all, I can't control what people say about those who use GAC, nor if people abuse the system.
My point is that people who genuinely need assistance to enjoy DisneyWorld can do so via the GAC, and thats great because everyone should have the chance to enjoy the Mouse's house
However, there may be others who, while they would not request a GAC, they would sit outside in the shade for an hour while a member of their party held a place in the unshaded lineup. Basically, they aren't so bad off that they need GAC, but they would take advantage of being able to walk to the front of the line. I just think you should be aware in advance whether you can handle the heat/crowds/walking without assistance (such as having someone else hold a place in line).
And frankly, I'd rather more people get GAC's than cut the line. As you said, its as broad as it is long, and perhaps the same number of people will end up ahead of me anyway, but at least I'll know its for a legitimate reason, and I won't be so ticked off when I see people strolling past me to the front of the line when I've been sweating in a slow moving line for an hour. haha
Last time I was at Disney was 6 years ago, and I honestly don't think I had anyone cut a line. One or two people per line wouldn't bother me, I understand someone needing to catch up with a group, but hopefully its not as bad as people say.