the point is also, that a 51% can't kill bitcoin actually, because it would only mean that its price will restart from one/zero, like a new birth, thus making pointless do a 51 only for killing it, normally one would do it for the money...
I agree a 51% attack doesn't kill Bitcoin. The network per si would remain alive. But if you can't do a transaction, Bitcoin is useless.
The issue is not about the lack of profitability of a 51% attack. The issue is more political. It's about doing a 51% attack to force you to use fiat money.