that’s a pretty shit argument… you could say the same about almost any law… this is why we have the legal system. who determines what’s fact? judges and juries… and you have laws in place in order to sort things out before the courts need to get involved
libel and deceptive advertising are exactly the same: who determines what is fact? courts… and people tend to do the right thing to avoid prosecution for the most part
and then you have anti-SLAPP laws to protect against frivolous lawsuits