I beleive that the big divide on this law and laws like it, is an ideological one.
There are people who beleive that individuals cannot be trusted, that they run amok. But the actions of groups - mitigated by a group decision making process, can be trusted and yield a better result.
It's about power being aggragated at the individual level or power being aggragated at the societal level.
The Florida legislation limits what a society can do to an individual by requiring probable cause before an arrest.
The people who don't like the idea of empowered individuals really hate that provision because it makes it very difficult for the masses to enforce their will upon those whom they disagrre with. It makes it difficult for them to punish a shooter they don't like.