1)
If laws are constantly being changed that hurts businesses and the population. Businesses don't know what to invest in because they're not sure whether laws will change and make the investment worthless. People also face day-to-day uncertainty because they're not sure whether what they are used to doing will soon be illegal. That harms the economy of the overall happiness of your population.
2)
If laws can be changed without providing proper justification, then Bad actors will be able to easily change laws for the worst , like Trump is doing