Spending capital to build hash capacity to protect an existing holding in BTC is inherently deflationary. Instead of "you need to spend money to make money" aka inflation/interest/growth, you have to spend money to keep money, which always reduces your holdings over time and turns the entire network over to companies that produce hashing capacity (hardware manufacturers, power companies).

But the initial assumption was that of an efficient market for hash power, which means the cost to hash is equal to the block rewards. And so deploying some capital to secure the network is nets zero loss.

That's a great way to lose all your capital, or force someone else to. You will probably not outspend a focused attacker or nation-state.