Expecting that is how you convince a large subset of folks to never bother with said deconstruction, and ultimately let bad ideas roam free and otherwise get adopted by impressionable / gullible minds.
Snark is there to suggest the reader go do their own research.
In a context like this, snark doesn't encourage people to "go do their own research" or save "impressionable / gullibile minds", nor is that really what people care about. (If it were, they'd expend energy doing those things in a way that might actually work.) Rather, its function is to vent one's own frustrations by translating them into concentrated language. The effect this has on community is to pollute it with fumes.
This is destructive of the ecosystem, unless one is happy with a single species, the snark, consuming all the others. Therefore we all need to find better ways of self-regulating and containing our frustrations. Then we can address other people in a way that has a chance of connecting with them.
Regarding the rest, I’m happy to simply disagree with you having observed this in practice in other communities. It’s not black and white.
As for flagging, what thread are you referring to?
And we all know that nobody is going to "go do their own research" because you snarkily disagreed with them. People do research when you make it easy for them to do, not when you drive-by insult them with an unreasonable reply. Drawing conclusions without providing reasons is literally being unreasonable.
There are billions of people with bad opinions on the internet. Nobody is forcing you to educate all of them. If you decide to try, it's predictable that you will at some point become tired of repeating yourself. At that point, you have two choices:
A) take a break
B) post crappy comments and justify it by saying you're tired