Not equivalent forms of logic.
I don't see how they're not. There's a well-known issue with an obvious proximate cause, but not everyone notices (or at least, not everyone complains of) the problem. You're asserting that, because the correlation isn't 100%, causation is impossible. Now, correlation doesn't prove causation, but less than 100% correllation doesn't disprove causation, either.
Though, really, 'whack-a-mole' gets brought up in more than just the odd isolated anecdote. Denying that it's a thing doesn't seem productive. Neither does dismissing the issue or any attempt at solutions by simply pointing the finger at the complainant.
It is often more advantageous to not use resources for healing at all, which also means characters aren't popping back up repeatedly as indicated by the "whack-a-mole" designation.
In those situations, where, for instance, PCs simply aren't dropped because they own the encounter from the beginning with good tactics, efficient use of resources for offense & mitigation, and general superior player skill (or just wimpy encounters), sure. That's pretty far from the 'more dangerous' feel that Psikerlord says he's going for, though, so I'm not sure how it's relevant.
Yes I find the game is far too easy with whack-a-mole going on. That's my main issue.
Would it feel more dangerous or harder with support casters healing allies /before/ they went down, instead? Because that's what punishing (or doing away with) heal-from-0 would seem to incentivize.
I want dropping hps to create a sense of urgency/suspense in the players - a feeling that this is dangerous combat. Whack-a-mole healing prevents that.
Proactive healing would also prevent it.
Maybe you should just cut healing word, give Cure Wounds a 1 minute cast time, and similarly adjust other healing abilities/items?
Healing becomes (but for the fighter's second wind, which is in no way whack-a-mole) an out-of-combat activity. Combat becomes more dangerous.