Maybe you thought that QSBS would keep being the way it was set. But there was a chance people would find QSBS written bad enough to change; I don't think analysis of that would show that no, QSBS is pretty close to being ideal from a point of view which well reflects opinions of people.
In a sense it's like an investment into an autocratic country - profits are high, but so also is uncertainty. In more developed countries uncertainty is lower - but it doesn't mean that laws are perfect.
From a general perspective, retroactive changes to the law aren’t a great idea. It’s one of many foundational philosophical realizations of the American criminal system that modernized it. So why do we accept it in the civil realm? There are variations here that are better.
I would say this change is more likely to actually entrench existing wealth. It would be better if adjustments to it were made:
* Disallow tax games with the QSBS. Currently if you carefully structure your allocation, you can get 30 mil or more tax free even though the limit is 10 (give shares to your spouse and a family trust - each gets an independent 10 mil). Tax games are an economic inefficiency that serve to entrench existing wealth holders and are parasitic on the overall economy (my tax attorney is not an important part of my investments or helping innovation in tech yet I have to pay him fees to figure out things that should be simple)
* Make the tax progressive like with income tax. 100% up to 10 million in net worth or 500k in salary all the way down to 0 at 20 million net worth or 1 million in income. At some point the government helping you become an elite investor isn’t necessary.
* Start the clock on when changes will be made impacting investments made today while changes are being debated. Then when/if it changes, make it retroactive. That way it’s done transparently with general knowledge in the market.
In a sense it's like an investment into an autocratic country - profits are high, but so also is uncertainty. In more developed countries uncertainty is lower - but it doesn't mean that laws are perfect.