This pretty much dissolves your only real objection, that we'd be keeping a ventilator occupied that would otherwise be in use. Nope. The solution to a deficit of ventilators is producing more - not letting people die without them.
Generally, you are trying to invent reasons and restrictions to make trying to train ventilator-operators seem like a bad idea rather than understanding or advancing how the idea might be viable. An example of this is how you acknowledge that training other medical adjacent professionals (e.g. vetrenarians) would likely work. Great, you agree the idea could work. If you expect that our capacity will be overwhelmed then presumably you think we should training additional operators. Instead of reaching that conclusion you imagine reasons to object to the idea though.
A SWE would likely be worse than a vet after a bootcamp. That's a good reason to have some entry requirements to the bootcamp and those requirements could be relaxed or strengthened depending on where we expect demand to be in 30 days relative to supply. A SWE through a 30-day bootcamp would likely be better than nothing.
The other main constraint you've imagined is that they would need to save more people than they kill to be worthwhile. No, they'd need to save more people than would die without them. If it would be better to just struggle to breathe than have an amateur operator, that would be an argument against them.
Your credentials, whatever they are, haven't equipped you to clearly communicate your reasons for opposing this idea. As I mentioned, it seems like you actually support some version of it.