RE: I don't understand the claims of "Steem is a Pyramid Scheme"

I don't agree with your idea of how adding value to Bitcoin works. You say that someone buying in with $100 would add $100 to the market cap but that's clearly wrong - it defines the value of all Bitcoin at the price they paid, at least temporarily. That could raise the market cap or it could lower it. If they bought a full Bitcoin for $100 the price just got cut to 1/10 what it was!
Think of it this way: if I buy in for a certain amount, someone else must have sold out for that same amount. The money isn't only moving into the system, and the system only grows if the seller sold for more than they bought for.