I think it's now beyond clear that they were planning on giving the keys to SS to Swanson from opening day next year. If that is a given, I see no problem with bringing him up now. He supposedly has 80 grade makeup, so I seriously doubt anything that could happen to him at the MLB level will hinder his development.
The argument should be whether or not he should have been counted on to start the year at SS next year.
If keeping him down for 2-3 weeks in 2017 gains an extra year of control then it was quite obviously a terribly shortsighted move done explicitly to sell tickets. In that scenario it is a truly indefensible move.
However, if the new CBA makes it so players need to be kept down in the minors for 3+ months to gain the extra year, suddenly this early promotion makes very little difference. There was likely zero chance the Braves would have kept Swanson at AAA for half the season anyways, so calling him up now loses the team no years of control.
I wouldn't be surprised if JS was privy to some info that strongly suggests the CBA will dramatically change the service time rules, and that inside knowledge was partly behind Swanson's promotion.