Great post. I've also been hearing from a lot of bitcoin maximalists - "why do you need to create a new coin?" The answer is that we've seen social networks try to use BTC-based incentive systems already and it hasn't worked (Zapchain, Changetip). These didn't even face the scalability problem because they didn't get enough traction - the bigger problem is bootsrapping the network. Someone has to pay to incentivize content creators! Users don't want to (mental txn costs) and startups don't have the capital .
Paying content creators directly from the blockchain is a very clever way to bootstrap the network, and you need a new token for that.
The best answer to such a question is this:
"Piling every proof-of-work quorum system in the world into one
dataset doesn't scale." - Satoshi
Bitcoin wasn't meant to be a social network / content network database.