This happened even in areas where holiday home ownership and rental was common as a business.
The failure of government to grapple with the negative effects of Airbnb is a separate thing. Airbnb are, in fact, in control of their own morality.
I think you'll find that zoning/planning permission is the real bad guy here. That and a failure to understand Adam Smith and implement the ideas of Henry George.
Then you're a landlord who has purchased more of a scarce resource than they require (a house larger than you need) who has then turned around and rented access to the extra you have to people who can't afford a home of their own, and in so doing have driven the cost of homeowner-ship just slightly higher, which was the reason you couldn't afford it in the first place. Repeat that a few thousand times and that's a huge contributing factor to why housing is in such a dire state here.
You haven't solved anything. You just went from being an exploited person to being an exploiter instead, taking advantage of people you should have solidarity with and inflicting the harm the system was inflicting on you, onto them instead. The system will continue feasting on people who can't manage the same as you did, and you now posses wealth you did not earn.
Even if that wasn't the case, I don't see a problem with buying slightly larger than is necessary, because (for example) perhaps they're planning to have a couple kids in the next few years, but will rent out the extra space until then. Moving is transactionally expensive, and expecting someone to move every few years as their space needs change is unreasonable.
Regardless, you seem a bit overly judgmental about this entire situation, and about someone you don't know at all.