It's fairly rational to point out that the market is overvalued at the moment to begin with. If anything, I'd expect some big losses in that 5% median if economic pressures leave people worried and speculating.
Not the original poster but I would point to the Shiller PE (i.e. CAPE) ratio as a useful indicator of potential over-valuation. The increasing cost required to make the same in earnings is disconcerting.
Stating that an opinion is rational does not automatically make it rational. Care to explain why you think it is?