I consider it to be valid.
To clarify:
Assuming someone's a sleeper is a pretty specific assumption.
That has very little to do with ages old umbrella projects (to which laymen 'understanding' added more bollocks than reality), the reality of groups of whichever agenda kidnapping children within compliant systems, or the price of eggs in China.
It's a very specific indoctrination, and one that is unlikely to manifest in this type of violence *within these circumstances and with no motivation*. These terms have connotations. It's not just goal-less violence - and one directed at civilians, working alone, and not having a safe route out after the act, either.
Hence my asking for another thread, and finding bad raising and other kinds of snap than being groomed for it specifically more likely.