What made him think that this was OK?

While forming a community with your neighbors can be a very rewarding thing to do, it is something that has to be done by choice and not by force. The main reason that so many people hate HOAs is that they impose their strict and sometimes unreasonable rules about what makes a good neighborhood onto every resident. If you don’t live with that, there may well be a person near you who has a similar sense of entitlement to do what they think is right, and if anything, it is all the more infuriating. They don’t even have the legitimacy of an organization behind them.

Within reason, a person should have the freedom to do with their property whatever they want. That includes whether or not they are willing to share it with their neighbors. Just because somebody doesn’t want to respect certain boundaries doesn’t mean that they have to put up with it, but it can be difficult to enforce this with an individual who lives close by and doesn’t appear to be interested in showing basic respect for the wishes of their neighbors.