In the early days of a site like this if a new user comes along and makes negative/snarky comments which don't fit the community it is pointed out, politely. Usually someone posts a reply friendly reminding that this sort of behavior is not welcome. This helps both the offender in question and lurkers to understand how to behave.
Then, at some point, people just snap. They've got enough, they don't want to help new people any more. Even though it has always been like that. Obviously, as the site grows faster users stepping out of line happens more often. So they start making 'everything's getting worse' posts. They are perpetuating the idea that all hope is lost.
So let me propose to try and tell people why they're wrong instead of just making a global assertion, even if true. Next time anyone wants to make a post how 'this community is getting worse and worse' instead try to salvage the discussion instead.