Folks doing this are fighting an uphill battle against stronger opponents who have powerful weapons (e.g., disable access), but it is not a hopeless battle -- there are examples of successful and profitable products built for filtering out force-fed content.
Actually, they don’t, as rulings in Germany have shown, Facebook does NOT have the right to close accounts "at will" or for ToS violations. Especially not if the relevant ToS paragraph does not conform to law.
(Just like you can’t refuse to serve customers for their religion in the US, for example)
If you go into a restaurant and put your finger in a fellow customer's food, that is not against the law, but the manager will throw you out. It's the same with Facebook's ToS, they can decide who and who cannot use their service. I have read a lot about how Germany has dealt with privacy within the Facebook platform, but have not seen anything about reinstating users who have breached ToS?
There were a few cases regarding the realname policy regarding that, and it’s still in the courts, but it looks like Facebook can’t exclude users for that.
FB ToS do not exist in a vacuum, which is why they always include "if a section is invalid others remain" or some such. Not sure about which jurisdiction the user / you are in, but in most areas signing up for a service does not obligate one to watch the ads (e.g., on TV one can turn away, turn off sound, blank screen, etc.).
I very much doubt that FB wants to fight, in courts, the person's ability to block ads on his personally owned display (both for bad PR and for uncertain outcome), thus their preferred response seems to be technological (make it harder or disable account they dislike) rather than legal.