if you get sick, you will produce an immune response, and your body will remember it. your body does not forget how to fight a virus, once it's seen it. those suggesting otherwise are pushing nonsense.
however, the virus is so weak, and so easy to clear without antibodies, that a very high percentage of people don't need to produce an immune response. most of the time, that's fine; your immune system just eats it, and that's the end of it, although there are also going to be a small number of people that go into septic shock. these are the really unlucky people - the ones that have bodies that don't respond to the virus at all, until it's too late, and then end up going into this weird reaction, where your immune system essentially commits suicide.
so,
a) you can produce an immune response. that's what being sick is.
i) you win
ii) you lose.
b) you cannot produce an immune response, either
i) because you don't need one, you clear it too easily.
ii) because your body doesn't recognize the new virus as a pathogen at all, until it's too late. then, you kill yourself off, involuntarily.
vaccination heavily relies on the feasibility of option (a).
but, this virus produces option (b)(i) so often that we should expect lower success rates than virtually any other virus we've ever seen - something that admittedly took me by surprise.
it's a virus that is, generally, weaker than the common cold - so long as we're strong enough to take it.
the only reason it's dangerous for the elderly is that they've never seen it before, and age reduces your ability to fight against new invaders. and, it is actually true that, when you get to a certain age, or to a certain advanced stage with certain diseases like hiv, you will die of the common cold - which is exactly what's happening, with this.
if vaccination is a coin toss, or worse, it's only going to be worth it for the weakest amongst us.
the rest of us will still need to fight it off - and may need to catch it a few times before we even have to.