You could say the same thing about a lot of things, including playing video games, posting here on HN, spending time with your family or kids, or anything else that doesn't directly make money.
If someone enjoys it, it's not a "wasteful time sink" any more than playing a crossword puzzle or watching a movie with your spouse.
>However if it is an /r/ for anything significantly popular, it quickly divulges it toxic garbage.
I disagree; /r/earthporn is significantly popular, and /r/aww is extremely popular. They aren't full of toxic garbage. When it's just pictures of cute cats, it's pretty hard to have a serious argument.
More focused groups, like the one for my car, aren't nearly as popular, but not everyone has the same interests, so of course a particular car-based subreddit isn't going to be nearly as popular as something that affects everyone, such as /r/politics.
Politics is especially bad because it literally affects everyone (there's no one now who doesn't live under some government), frequently in a rather profound way (the laws that are passed will directly affect your livelihood, and could put you in jail or get you killed), and our leaders are mostly a bunch of sociopathic, corrupt, evil people, and on top of all that, none of us (assuming you're an American, as /r/politics caters to American politics) can remotely agree on how our country should be governed (some people want outright communism, others want corporate fascism, others want democratic socialism, others want a theocracy, others want near-anarchy).
So in summary, if you want to avoid "toxic garbage", it's pretty simple: find a forum that's full of very like-minded people, and avoid anything that delves into politics. Or if you want to talk about politics but avoid nasty arguments, make sure to find something close to an echo chamber for your preferred candidate/party/orientation.