investment is an important way that money flows around an economy. safer investments tend to move money slowly… if people think conditions can flip on a dime, that adds risk and more risk leads to people making otherwise safer investments (this goes double: more risk usually means more reward, so if you increase baseline risk then you’re negatively effecting both sides of the equation)… we do things like grandfathering in laws because of someone in good faith invests in something it’s good to have reasonable expectations that they’re not going to have the risk calculation changed underneath them - otherwise you have to take that risk for all classes of investment, and that’s far worse than the small (probably ~10 year) loss from not catching out the practices you’re trying to change in existing activities