I find this to be a fairly simple equation, (but admit that others come out on the other side). If I have two kids, and want to engage in a behavior that is assured to result in me accompanying one child while leaving the other child unattended, I am going to accompany the child who is going to be in the unsupervised environment (i.e., "in the crowd") and allow the child in the "captive" environment, (i.e., the attraction) to be the one who is alone. Far fewer bad things can happen to the child in the captive environment than can happen to the child in the "free range" environment. I trust, (and I use this word loosely), the other guests who are riding the ride with my unattended child more than I trust the general public who would be surrounding my unattended child in the crowd. The guests on the ride are far more apt to appreciate that they are being watched and monitored by security cameras on the ride and are less likely to pose a threat. Guests who are milling about in the crowd? Not so much. This applies in each and every circumstance as long as the child who will be left unattended is old enough and mature enough to be unattended. Given Disney's age restriction for riding solo, this doesn't come into play. In other words, I would never accompany a 16 year old who didn't want to ride while letting a 7 year old ride solo. But Disney does not allow this, so the point is moot.