The government has to be able to actively respond to the problems of the moment, and those problems will constantly change. A handcuffed government only benefits the already-powerful.

The dirty secrets of the "but the founding fathers!" argument are that (a) they knew they weren't creating a perfect set of rules in the Constitution, and planned for us to be modifying it as we learned new things and the world changes, and (b) it's failed anyway. Abstract principles listed on a page don't "protect freedom," bad actors can find ways to sneak things through (sometimes in plain sight, like that whole slavery thing that took a century to get figured out, or the followup forms of discrimination that are still with us).