If the product you're using is free, the information you enter is what's being sold to someone else.
Even paid services can and usually will sell your information, so just assume that everything that you enter is considered public information from that moment on
Tell me you don't know xkcd without saying you don't know xkcd. These comics are licensed as CC-BY-NC 2.5, which means you are allowed to remix and use them, without explicitly asking for permission, as long as you attribute the original/author (which is given here) and as long as you do it non-commercially (which is given for this post IMHO).
If you do not object, they can and will use your data, posts, images,... to train AI on it.
When you object, they (pinky promise) won't do it (knowingly - they say you may end up in their training material if e.g. a friend of you uploads a photo of you but doesn't tag you)
Anyone remember or been to those markets in eastern europe, where you could buy bootleg CDs, copied CDs, cracked games, counterfeit products, etc?