> Shouldn't the safety regulations be the same no matter what?
No. Hotels are denser (in terms of people sleeping in a building) than typical apartment buildings, because apartment buildings need to devote the square footage to copies of kitchens etc. per apartment, which unnecessarily would drive up the cost of hotel rooms. But leaving that aside (after all, the argument is about apartment buildings being used in place of hotels, not hotel buildings) - there's a bigger picture than just safety regulations.
How about taxes? Cities which attract tourism often like to establish high taxes on tourists, because municipalities need to draw their budget from somewhere, and tourists don't vote (well, they do, because they could decide to vacation somewhere else, but barring a very steep price increase, tourism tends to be somewhat immune from these higher taxes, by the very nature of most tourists saving up money to travel to some specific fantasy location), so municipalities will levy high taxes on hotels, knowing full well that those taxes are passed on to tourists. When hotels start to be threatened by unregulated competitors, that competition threatens that tax revenue stream.
> As for zoning laws - those are arbitrary lines drawn by the city planners
So what? As many objectors have pointed out, city residents have an inherent interest in developing a sense of community, which requires people to commit to living in apartments over the long-term. Ghost ownership threatens that social good, and seasonal tourism threatens local mom-and-pop shops serving local neighborhoods, which no longer get foot traffic in the off-season. That's not to say hotels are evil - it's to say that one of the central tenets of urban planning is to attempt to balance competing, mutually-exclusive interests forced to live together by inherent urban density, for the common harmony and benefit of all, and zoning is an integral tool for that purpose.
> As a property owner, you have to make the best use of the property, and if airbnb brings in more money, you _have_ to do it, otherwise, you'd be losing value.
This is a farcical argument. The highest return for urban property is turning it into illegal drug factory. By your logic, investment apartments should always be turned into illegal drug factories, because their investors have to do it, otherwise they'd be losing value. After all, what's the qualitative difference between breaking zoning laws and breaking drug enforcement laws? If you're OK with operating an illegal hotel, to the detriment of the people in the surrounding neighborhood, then why not be OK with operating an illegal drug factory, also to the detriment of the people in the surrounding neighborhood?