1. I'm not sure we agree on that... Bitcoin doesn't protect against attacks, it provides you with a relatively simple model to measure the cost of attacks.

At equilibrium, any Bitcoin network participant will look for two fundamental things: (a) being able to move their own assets and (b) relative market price stability of their bitcoin. In case of a sustained 50% attack, both properties start to crack, but not completely. But after the attack, they are regained -- (a) immediately, and (b) eventually.

Consider the attacker to be a government, for example, an actor with a relatively high amount of resources, and the Bitcoin participant a dissident citizen of such government. The dissident wouldn't like to have its assets frozen by the government (through strict censorship of the dissident's transactions), so the market value for Bitcoin drops comparatively to how wealthy was the dissident selling its bitcoin savings. But, also, the dissident might avoid selling if they have enough financial capacity to withstand the attack.

In order to carry out such attack, the government needs to increase its energy spending on Bitcoin, up to the point where the attack is successful for a prolonged period of time. Bitcoin production is intrinsically bound to energy generation, thus to its economic realities (variability of demand, climate conditions, political affairs, just to name a few).

It would cost a government X dollars a day, or Y watts a day, every day, minus the price of the coins generated to attack the network. I estimate X to be the total miner rewards: at the time of writing, 38M USD [1]. Y seems to be at around 456 GWh [2]. Is it worth it for your adversary? That number is the dissident's security parameter. As long as their savings are less valuable than the cost of the attack and they can sustain the attack financially, the dissident should be fine (or really scared about an enemy irrationally spending a lot of energy/money with the purpose of just preventing them to access their money temporarily).

In the end both miners and users just want the chain to move forward. If one particular actor or coalition potentially prevents it, users/miners outside the coalition (if they detect it) would raise their investment to continue chugging blocks.

I think there are no "legitimate" vs "attacker" uses of hashing power. It's more about coalitions between miners and how costly/profitable would it be for them to centralize the network, and how hard is it on the other participants to coordinate a decentralized counter-attack (which ends up profiting them). But eventually, the equilibrium between all participants is to spend as little money/energy as possible. And if it's not decentralized it becomes censorable: next, it loses its value: now who's gonna want to mine something worthless?

2. We see it the same way. I'd add that if Bitcoin is staying around (I don't think it can be shut down), one solution is to use Open Timestamps or other hacks that don't require "block real estate", thus in no way compete with transactions, essentially piggybacking the PoW and getting the timestamp for free.

[1] first result I got for "block rewards Bitcoin last 24 hours": https://bitinfocharts.com/bitcoin/

[2] first result for "24 hour bitcoin consumption watts": https://digiconomist.net/bitcoin-energy-consumption