how do you know what threats I face? how do you know what threats journalists and whistleblowers face?

this is approximately the same discussion as with ECC RAM: the benefits vastly outweigh the slight performance loss and die area increases.

ECC passively benefits everyone, even people who don't know what it is or why it's useful. Anyone can be a victim of random bit flips, it's not a targeted threat.

Memory encryption, on the other hand, provides absolutely no benefit to 99.999% of users. If you consider yourself to be such a high value target that you suspect someone might gain physical access to your hardware without your knowledge and carry out extremely sophisticated hardware attacks to extract your data, you are a tiny minority and it makes sense that such niche protections would require buying specialized hardware. Even then, the odds of such an attack being chosen instead of a far less sophisticated software-based approach are also tiny.

Of course, if the hardware itself supports the feature and AMD simply decided to disable it, that's still a shitty thing to do, but let's not pretend that it is in any way comparable to ECC.