By joining a HOA, you've delegated away to the collective the right to dictate to your neighbors what they can and can't do with their own property. In your case, the system worked - because you are in a HOA. If people want to exert that kind of collectivist control over their neighbors, that's the kind of organization they should be buying homes in.
But outside of that structure, what gives someone the right to dictate to their neighbors what they can and can't do with their own property? All kinds of small businesses are routinely run out of residential zoned properties. "Renting a room" seems like the kind of small business that's ideal for this situation - it takes no more infrastructure to house a vacation rental than it does to house a longer-term resident. "Hotels" require employees and elevators and truckloads of supplies delivered weekly; vacation rentals have none of that, and so the comparison makes little sense beyond "they are noisy". Leaseholders can also throw parties and be disruptive; there is an existing legal process to deal with noise complaints.
This category of complaint seems like a thin veneer around the core of truth that people who sink a colossal chunk of their nest egg and future earnings into one asset are knee-jerk averse to anything perceived as a threat to it.