Raising taxes on those future cash flows makes the assets less valuable today.

The contemplated change isn’t this drastic, but imagine that you have an asset today that’s worth $X. Suddenly, overnight, everyone in the market for that asset learns that all future benefits from that asset will be permanently exactly half as valuable as they were yesterday. What would you expect the price of that asset to reconverge to? I’d expect it to converge to pretty close to half of $X.