I'm a big proponent of the bear case, but if you factor in dividends [0] pretty much any time in the last century has nominally been a good time to invest in the S&P 500 even if the first few years aren't optimal.
The bear case is generally "this will cause a crisis, then the government is going to print money, hand it out to asset owners & lump taxpayers and citizens with the real costs". There has been a reasonable expectation that shareholders will come through fine since the '08 crisis firmed up expectations about how the government will handle problems. I don't think there is an expectation any more that the S&P will go down in nominal terms. To argue that it will someone has to come up with a theory where the Fed doesn't get involved. There have been multiple major crisii and if anything US stock market performance is the inverse of how the economy is expected to perform. For example, COVID was a big winner for shareholders and asset owners despite obviously being an economic catastrophe.
The bear case is generally "this will cause a crisis, then the government is going to print money, hand it out to asset owners & lump taxpayers and citizens with the real costs". There has been a reasonable expectation that shareholders will come through fine since the '08 crisis firmed up expectations about how the government will handle problems. I don't think there is an expectation any more that the S&P will go down in nominal terms. To argue that it will someone has to come up with a theory where the Fed doesn't get involved. There have been multiple major crisii and if anything US stock market performance is the inverse of how the economy is expected to perform. For example, COVID was a big winner for shareholders and asset owners despite obviously being an economic catastrophe.
[0] https://www.slickcharts.com/sp500/returns