Why have steem power at all if you or someone else can decide that I am not allowed to use my power as I see fit?

I'm saying the exact same thing right back at you: Flagging, just like upvoting, is me using my Steem Power as I see fit. What gives you the right to stop me?

Your market metaphor is not apt. The Steem marketplace has a fixed maximum daily sales amount that is rewarded based on the relative Steem Power being flexed behind each piece of content. No flea market or farmer's market works like that. Hence, your comparison is just not apt. It doesn't work.