Yes, decentralization is everyone, even the sellers, but decisions (voting on content, proposals, witnesses) is done with Hive Power. I offer more support those build stake to participate in governance. Milkers are welcome to use the chain as they see fit; it's a free market like you say, but I will prefer to offer my support to people who participate by staking their HIVE. I won't downvote sellers; as I said, selling is not wrong. I just have a preference of what kind of Hive citizen I support.
Also, recent analysis by the likes of @azircon that demonstrates that MOST folks in the top 1,000 are, in fact, staking HP. He calls it the Krampus Coefficient. 84% of accounts are holding what they earn or a little more. So I disagree that holding is for the few.