SMT is not a bad idea.
As usual, sweeping generalisations are worse than useless. SMT is not a bad idea
in principle, but most software is not designed to take advantage of its shared L1 cache, which means that leaving it enabled often makes things slower, not faster. Two unrelated tasks running on the same core means less cache for each.
Intel's version 'hyperthreading' is also not a 'bad idea'. Intel's problem is that it left their chips vulnerable to Spectre, Meltdown and Foreshadow. The fix they applied ruined performance. But that's an Intel problem.
Where do I begin?
First of all, at least some variants of Spectre affect AMD as well. But that's actually not very relevant here because none of these CPU bugs are specifically about SMT. SMT makes them easier to exploit in some cases due to shared cache, but the bugs are fundamentally about speculative execution and cache side-channel attacks.
Turning off SMT will not turn off either of these things, it will only eliminate the possibility of leaking secrets between threads via the L1 cache, making some exploits more difficult and some mitigations more effective. Notably, it does not stop leaking secrets
within a thread (hence mitigations like retpoline) or between cores via the L2 cache (an area of ongoing research).
I really have no idea why anyone would buy Intel on a mainstream desktop right now when Ryzen offers so much more bang for buck.
Someone's been drinking too much kool-aid...