The FAA data shown earlier shows 64% of the training accidents were loss of control on landing or attributed to xwinds. Neither of these are specific to T&Gs.
Oh? Do the FAA data break out touch and go landings vs full-stop?
There are differences. A touch & go is busier than a full-stop landing, because the pilot is occupied by cleaning up the airplane and re-accelerating towards takeoff speed. This division of attention
lends itself to a sloppiness in directional control, something I can sometimes see in rated pilots.
The more complex an activity, the higher the probability of screwing it up, for any fixed level of skill, a fact that should be self-evident. The only thing that's really debatable is whether the increase in probability of an accident is significant or not. I don't know the answer to that.
The details of the accidents at my flight school aren't relevant; the students lost directional control while doing touch & go's. Whatever the conditions which may have existed at the time, many people felt that the students might have been more attentive to controlling the aircraft had that been their sole objective, rather than trying to take off again.
Training issue? Yes, of course,
every pilot error is a training issue. Soloing students is about sending half-trained pilots out to gain more experience under controlled conditions. For any maneuver, they have a higher probability of screwing it up than a pilot with more experience. We must accept that if we accept the concept of a student solo. It's not unreasonable to improve the odds by restricting them from the activities where the chances of failure are highest.
I am not arguing in favor of preventing students from touch & go's, I'm only arguing that it's a reasonable restriction. Personally, I'm happy to have my students do T&G's, but they generally have 20+ hours before they solo.
