You're missing the point of stricter gun control laws. No one thinks that criminals will just "follow the laws" and give up their guns. The point is that the vast majority of armed criminals don't machine the weapons from the metal on their own. There is a supply chain, and some link in that chain are not criminals. Stricter regulations will impact that supply chain and make it harder for people to obtain guns who shouldn't have them. (It's also not "all or nothing"; we don't need to ensure that no criminals ever acquire guns. Any reduction in the number that do saves lives.)

Laws restricting public carrying of weapons aren't geared towards stopping career criminals, they're geared towards preventing injury and death caused by "lawful owners" accidentally, or intentionally but recklessly, firing their weapons in public, thinking they "needed to" or "should" do it. If someone wants to carry a firearm in public, it means they believe there is a situation where they will need to fire it in public. And as we know, humans are fallible and often think they "need to" do harmful things in situations where they don't. Those cases are what public carrying laws are intended to curb.

(BTW, most deaths due to firearms occur not by thugs/gangsters/career criminals, but by lawful and, prior to the incident, "responsible" gun owners making mistakes.)