Unfortunately, once you share something online it's moved beyond anyone's control. Even if the platform respects your wishes and does everything right, there's always 3rd party web crawlers, data harvesters, archival services, etc. They are always around, busily vacuuming up everything they can on the web. Few if any shared posts or comments will ever be truly deleted. Storage of text is cheap, and a lot of entities love hoarding data.
So, try to only post stuff you wouldn't mind your parents, coworkers, friends, etc. knowing about. Corporations and governments are moving more and more towards 100% surveillance and away from privacy and anonymity. It's a giant problem, and I hate it. But the only element of this you can control is your own behavior.
I do this, too. I've noticed local companies who advertise heavily on local TV/radio often charge 2x as much as the competition who don't. And the aggressive advertisers are often arrogant and difficult to work with.
And it pisses me off when I see giant insurance companies spending millions on celebrity spokespeople and Superbowl ads. That represents a lot of denied claims.
Beyond all that: fuck reddit. Don't give money to spez.