For some reason I added my previous comment to the wrong area haha...
Wanted to add a few things as to why stocks could go higher, and what people are missing when they compare this to 2000:
A. When I said yields are low, I meant that people will chase yield and mostly on stock price appeciation. However SPX still yields more than 2x the 10Y bond and is still 70% better than where it was in 2000. Yet this isn't just it... Big companies can borrow more money and perform well, while their competition can't. Essentially this makes these companies too big to fail and explains the appreciation
B. Many people use various metrics to compare this bubble to the previous ones. Yet I think 2000 and now is very different as based on many things, stocks aren't that overvalued. What do you compare that to? If you think of stocks based on Gold, the global money supply or US M2, the US10Y etc... you quickly find out that stocks aren't that expensive. Also just looking at what worked in the past once isn't enough and especially if the conditions were very different.
C. US companies dominating, US people having an investing culture, people buying indices and holding them passively (not management, no selling), stock buybacks, the USD losing its purchasing power, people believing the Fed has their back, investors front running inflation, easier/cheaper access, retail getting in the game etc etc. These all sum up my points above, so you can see it isn't all just doom & gloom. Things don't repeat the same way they did before, and if most people expect things to go down because of similar previous situations... then most of those people have sold or are short, meaning that they are the fuel that pushes the market higher as they buy back much higher.