I would like to see this mythological kid who gets thrown out on the court and has his confidence destroyed. Who is he exactly? Names? Anyone? I call strawman.
We don't actually need confidence destruction as a reason not to push Singletary into the starting job. I see two reasons that are related to, if not exactly identical to, the reasons you gave:
a) there is no guarantee Singletary even makes the squad
If we had nabbed one of the top-tier PGs in this draft (Rose, Westbrook, Augustin, Bayless, and even Mayo/Gordon if that's where you're trying them) then, yes, it makes sense to throw them out there. We would be committed to them as a high pick with a large amount of talent and we'd trot them out there even if they struggled in the hope that they eventually live up to their potential. We are not likewise committed to Singletary, even if he does make the squad. If he struggles, we move on. And we don't want to have to deal with rustling up a starting point midseason if we can avoid it. Better to let him backup, and take over if he's capable.
b) ... let the fans see an old fav ... a guy who would not necessarily interfere with a young PG ...
Exactly. There isn't a bargain basement PG out there that would be more appealing to the casual fan. Appeal to the casual fan means: butts in seats, TV ratings, radio ratings. Increased revenue based not on the probability of winning night in and night out, but on nostalgia. A lot? Probably not. But almost certainly measurable. And if we're looking at 30-odd wins any way you slice it, I'd rather see J-Will and an extra mill or two in the team coffers than Singletary or Anthony Johnson or Chris Duhon or you name it -- so long as J-Will isn't allowed to stunt Singletary's potential growth as mentioned above. That cash could be the difference-maker in a FA signing down the road.
The first is a good reason to sign any vet rather than start Singletary, the second is an argument directly for J-Will. I'm not J-Will or bust, but unless something somewhat unexpected comes up he's likely one of the best alternatives unless he prices himself out of our range.