Is my house unlocked because I have the key?

Buddy, you are lost. Why do you hold a private key if not to prevent the money from moving?

Locking is not a stupid thing to say. In fact, it's quite precise. A channel is money locked in a 2-of-2 multisig, where you do not have one of the keys. Your funds are only unlocked if your counter-party cooperates, or after the CSV delay.

Yes, for two reasons.

1. More payments will naturally flow through nodes with more channels and liquidity. For example, an LSP will route more traffic than a raspberry pi with two channels. This is inherent and good.
2. The protocol does not give a node a reliable way to find a feasible path to the destination. Each channel a payment is routed through adds a risk of failing due to insufficient liquidity, which means longer payments routes are exponentially less likely to succeed than shorter routes. Generally speaking, there are two mitigation's to this: make bigger channels and prefer shorter routes during path finding. This is bad centralization.