What Mighty is trying to do is
make the web faster for people who really need it to be really fast, and offering people the opportunity to voluntarily pay a modest monthly fee for that service. If there is a reasonable way of saying this should not be done, sure have at it. Or just let customers decide. Whatever you like.
I get that much of the rage is focused on the some variant of the complaint that the web is slow because of JS cruft or advertising or whatever. Fine, there's a place for a discussion about that. Mighty didn't create that problem. They're just offering a solution that problem for people who need the solution enough to be willing to pay for it. No need to wish for Mighty to "crash and burn" just for trying to offer one kind of remedy.
As I said, it doesn't matter what you do - the good founders will either read your criticism as helpful feedback and improve, or they'll recognise it as being from a "hater" and ignore it - perhaps being a little bit more spurred on to succeed. It's just up to you as to what kind of help you want to offer that founder.
As for your last sentence: in this discussion we're talking specifically about the kind of feedback that is levelled at the founders of nascent products/companies when they launch, when they're just trying to offer something new to people who might want to try it. But even aside from that, in my experience, people running companies aren't usually hoping their competitors "crash and burn" - people who think like that are ego-driven and don't make it very far. There's generally a sense of respectful rivalry between competitors in an industry, and usually one company hopes to succeed at the products they make, whilst other companies in the space focus on different products or market segments.
I guess it's all about whether your outlook is constructive or destructive.
Ultimately, if we're generally in agreement that it's not commendable to be a "hater", then all other discussion is fairly arbitrary.