There was/is another thread on this. You can't tell from the newspaper article ("fish tailed" then "nose dived" ) eyewitness on local TV news (okay, not necessarily the best, but the guy looked at least somewhat knowledgeable) stated the aircraft was at a low altitude, lost power and then stalled started to spin and went in tail first.
Back to the question of ex-military aircraft and civi/low time low currency pilots. In military pilot training the curricula generally call for about 300 sylabus hours in the aircraft and a load more in simulators plus classroom work and homework before one gets into the first "fast jet". For a variety of reasons the actual hours the student has are almost invariably significantly more than the sylabus hours.
For aircraft that are jets exmilitary trainers like the L-39, Hawks, T-37s, etc it is not unreasonable for an experienced pilot with an adequate checkout and reasonable currency to be able to safely pole around in day VMC. Go from there with respect to aerobatics, etc. I would be very leary of blanket prohibitions etc, and as has been pointed out on other threads antics in these and higher performance aircraft are self limiting by the cost involved, lack of available insurance, and limited number of aircraft available.