Okay, I'll play devil's advocate for fun. Let me say first that I don't dislike the new law on principle of gun-toting-ness -- that's fine IMO.
Here's the rub, legally speaking, and I don't know what the final outcome might be. Essentially, you have a legislature telling landowners that they must allow people to bring guns onto their property. Now, folks, what we have here is a clash of rights: your rights to bear arms vs. someone else's rights of property.
My first inclination is that if I own land, I get to say who comes onto my land and what they can bring with them. The government should stay out of that issue. It could be (and perhaps will be in court) argued that this is a "regulatory taking", an exercise of some sort of eminent domain whereby the government, by passing a rule without actually possessing or reallocating use of property, exerts authority over one's own rights to that property in such a way as to fundamentally diminish the owner's rights over his own property. Here, the government has taken the authority and right of the landowner to determine what items are brought onto it and has given that authority to other private citizens without compensation.
Regulatory takings are common. But, they are takings, and they still have to pass constitutional muster. This law may be aimed at reducing crime, but I doubt that the Attorney General of Florida will be able to demonstrate that any quantifiable decrease in crime will occur sufficient to override the property owner's interests. This is especially true here where there is no compensation for the taking, let alone no "just compensation".
On the other hand, after the Kelo case a couple of years back (you remember, the one where Wal-Mart successfully convinced a city council to wipe out a poor neighborhood so they could put a store there, and the Supreme Court said it was okay to take private property for economic development), there was a backlash of sorts. State legislatures passed laws doing lip service to limiting government authority to do that, and people pretty well just gobbled that up and forgot about it. Well, the President of the United States did as much, and here's what an executive order he signed says, in part:
Section 1. Policy. It is the policy of the United States to protect the rights of Americans to their private property, including by limiting the taking of private property by the Federal Government to situations in which the taking is for public use, with just compensation, and for the purpose of benefiting the general public and not merely for the purpose of advancing the economic interest of private parties to be given ownership or use of the property taken.
Two things to note: 1. Just compensation is required. 2. "Public use" is for the "purpose of benefiting the general public". Now, that's very unclear and that lack of clarity is exactly why the order is meaningless in terms of limiting authority, and it was just a feel-good order to placate conservatives who recongized Kelo as a very dangerous precedent ..... one which still stands untouched, by the way. The order did nothing in any realistic, practical terms. But, what is does reveal is that the Federal Government --- and, in turn, local governments --- view of its own authority is that as long as the only purpose is not to funnel an economic interest of a private party without some minimally justifiable public interest, then the taking is okay, but there must be just compensation.
Flash forward: Here, the taking is not for a "public use". There is no evidence that public use of private property will increase in quality or kind for the public benefit. And, again, there's no compensation to the landowner for confiscating away his right to say who comes onto his property and with what. What this is is an election year feel-good law for Republicans in the Florida legislature who, even if the law is invalidated, win the rhetorical battle in their campaigns. Smart political strategy, very questionable constitutionality of the law itself.
I may very well have this wrong legally, but on first blush, this law looks like bad law. There are other ways to accomplish the stated goal. First, to the extent that gun-toting liberties are eyed for protection, the Legislature could pass a law that simply says that no business licensee may refuse service to any person by reason of that person's possession of a firearm while conducting business with the licensee. That's different because it is not aimed at property owners' control of property, but it is aimed at a term of state/local licensure of businesses. It also applies to businesses that don't necessarily conduct their affairs on their own land at the point of service, i.e., sales routes, online businesses, etc. So, you have the added feature that this is not about control of landowner rights at all. Seems to me that's just one way of getting there on a slightly different path. BUT, these legislators know full well that to pass such a law will create administrative burdens on municipalities who license businesses, that to some degree the very conduct of non-discrimination against gun-possessors would have to be accounted for in the process of business licensure, and they will not make local governments unhappy with those burdens. It is just too politically costly. Therefore, they do something that gains truckloads of brownie points with voters and costs them nothing politically with the bureaucracies that they deal with most. Whether they succeed in getting to their constituents what they are pushing is of no import -- they win anyway.
Human government bears the same relation to hell as the church bears to heaven. (David Lipscomb, On Civil Government, 72).