This is all fine, and bubbles do pop. But look at the DJIA, nearly every point looking back looks like a bubble. So if bubbles pop do they drop to zero? Or can we say that while the highs we see today may drop compared to where they are now, that we have continued to move the average in the right direction?
My second point is, it is also hard to tell if you are not in a bubble, and you won't know until retroactively you see why.
The only sector that doesn't seem to be doing well right now is the agricultural sector but it's only 1.3% of employment compared to like 30% in 1929, so I'm not too concerned, the stock market seems grossly overvalued - this does concern me.
You really should plot it on a log scale when you look back. And the Dow is interesting because it's been around so long, but it's a really bad index. It's cost-weighted, probably the most naïve way to weight an index.
My second point is, it is also hard to tell if you are not in a bubble, and you won't know until retroactively you see why.