I certainly do not want to see a crash. Would prefer to see low volatility.
If it falls, it falls, so be it. But "crashes" do in fact do damage to the real economy by denting consumer sentiment and demand.
Yes we all want to buy when the market is low, but I think it is poor form to want to see wholesale wealth destruction across the population.
I'm hoping that MMM's original comment was somewhat tongue in cheek, intended to jovially nudge people into not worrying too much about when to invest, and to remember that low stock prices are good for investors. His other posts seem to indicate general goodwill.
Regarding wholesale wealth destruction, it seems to me that true wealth is physical capital (tools, natural resources) and human capital (people with skills), which do not disappear just because stock prices go lower.
It also seems that both high and low prices have trade-offs. High prices encourage investment and risk taking because people feel success is in the air, but if prices are too high, some people take foolish risks that should not be taken. Of course, as the quoted poster implies, low prices discourage people who should take risks, leaving their ideas and talents unused. Somewhere there might be a best equilibrium that maximizes good risks and minimizes bad ones, but in practice it's probably hard to find.
In any case, low stock prices and economic growth can occur together. The 1970s had terrible stock prices in America, but living standards rose and wealth inequality was low. If rising US interest rates come about as planned, we could soon have falling bonds plus falling stocks plus a growing economy - disappointing for people living purely from their capital, but good for everyone else.
Personally, I think the curve of danger on each side is pretty shallow, meaning we can tolerate fairly low or high stock prices without undue impact. Think of it like winter and summer: the peak of summer can cause more wildfires, which are dangerous for a time, but you need a few fires to keep the brush in check and the forest balanced. Similarly, freezes kill the damn mosquitoes - a good thing! Learning the lessons from each season keeps us healthy year round.
One poster's opinion, anyway. Cheers.