If the ask is, why was the hardware like that in the first place the answer is because it can’t be fully validated.
But that's not the question. There are two questions: Who should be responsible for patching hardware vulnerabilities? And if the answer is "the kernel" then should speculative but never demonstrated vulnerabilities be patched? Linus' answer is the hardware manufacturer, and no.
Is this really the hardware vendor’s problem though? It’s the consumers problem.
Maybe we're running into the ambiguity of language. If you mean to say, "Who does it cause a problem for? The consumer." then sure. On the other hand what I mean, and what I think Linus means, is "Who's responsible for the vulnerability existing? Hardware vendors. Who should fix it? Hardware vendors."
If the ask is why should a speculative fix go into the Kernel [...]
Depends on what you/we/they mean by "speculative". IMO, we need to do something (microcode, kernel patches, whatever) to patch Spectre and Meltdown. Those have been demonstrated to be real vulnerabilities, even if no one has exploited them yet. But "speculative" can mean something else. I'm not going to read all the LMK emails so maybe they're talking about something else. But I've seen plenty of, "Well if X, Y, and Z happen then that could be a vulnerability." For that kind of speculative vulnerability, one that has not been demonstrated to be a real vulnerability, I am sympathetic to Linus' position.
The person who uses the shitty tool is a moron. The person who makes the shitty tool is an asshole. At least in this case where the shitty tool is actively promoting shitty PRs.