Edit: as noted below, the implied question is: what "legimate health concerns" exist for short-term renting but not couchsurfing?
I thought it would be instructive for people who talk about "government" as if just putting the word big in front of it solves the issue, and the solution is cut taxes for rich people. None of that has anything to do with this. This is a concrete policy change in a specific area.
If you allow people to not be present at all, then some will turn this into a business and operate a real hotel room, 365 days a year. Operated like a cheap hotel. I can see why the government may want to regulate that.
An easy way to distinguish the above situation from legitimate friends staying over, is to ask for the owner to be present. Or couchsurfing. That tends to make it a more casual and better controlled environment. I can understand why the government may want to stay out of this.
My impression is that the real criteria should be how much the room is rented: if you have guests 300 days a year, you should be regulated. If it's 10 days, leave me alone. The problem is that it's probably hard to define, and may impose its own set of requirements (such as, everyone would have to keep a registry of all visitors, just to prove that they don't fall into the hotel category).
I don't think this is a totally absurdly black and white case, it's no oppressive regime rearing its ugly head. Both sides have ulterior motives (AirBnB and the established hotels), but their arguments aren't totally without merit. And one thing that people keep forgetting, is that this law isn't breaking new grounds, both renting and hotels are pretty heavily regulated, mostly for a good reason. Yes, for the hard-core magical hand of the market libertarians this is another nail in the coffin, but I bet that a lot of people that get too angry in this discussion don't have problems with laws against arbitrary landlord decisions or hotel health and emergency codes.
Let's keep this reasonable…
Says who and what are those reasons? I suspect the reasons are: old people got scared and stakeholders saw an opportunity.
Luckily the Internet is mostly protected from scared old people and powerful stakeholders.
Maybe in another decade when we're all older we will be willing to give up the freedoms we once enjoyed when the Internet was still young. And it will be for "mostly good reasons."
Remember the old silent movies, where the evil, mustachioed landlord was one the most popular villainous archetypes? That wasn't without reason. People looking for a roof over their heads often aren't in a good bargaining position, so often you could make them sign almost any contract. There are quite a few federal and local laws that limit what's possible in all these cases, so that your landlord e.g. can't evict you all willy-nilly. Rent control is also rather common.
Same goes for hotels, especially when it comes to security (emergency exits, maximum occupancy etc.).
Whether every single law (including this new once) make sense is another question, but my point is that this isn't something completely new, were all of a sudden the octogenarians ruling the world decided to come down on the poor cyber-startups.
What that doesn't mean is freedom to gather with a bunch of friends where and whenever you want. What it does mean is the legal right to stage peaceful protests or gather in public (with reasonable restrictions).
If needed I can run over to the library and grab you a list of cases on that, but I think you'll have trouble finding any for "couchsurfing."