l know this is a stupid question, but can you just go out and climb in yosemite or something, assuming you have all the gear and knowledge to not kill yourself?

Unless u r guiding other parties, there is no license or certificate needed. In fact there really is not any enforcement of guides & training other then on some climbs on federal or state lands which will regulate guiding businesses.
Some high use or fragile climbing areas may require a permit only for the limitation of numbers of people on a particularly popular route, There also may be restricted times of the year for the preservation of different species of birds which r nesting, or at sites like Devils Tower where they used to be a climbing moratorium during Indian rituals.

In the US, there is not any official certification required (like other activities like Scuba, etc). Most climbers do not have any official certification unless they are a paid guide and responsible for the safety of paid clients. Many have taken classes ( l have taken them), but most do not offer any kind of licence or certification.

http://alpineskills.com/rc_private.html

Good Luck

there is no licence to be an offical cliber but there is one if you want to guide and some places require you to get a licence to climb

Yeah it is only places like Everest where the government puts loads of red tape so u need to buy a permit to climb there where u need anything.
In climbing havens like yosemite u can just rock up with ur gear & start climbing.
As for qualifications for professionals, l assume they only need qualifications for insurance purposes for their clients. so as long as u have no clients, u can climb wherever u want! (barring nesting restrictions, trespassing, etc.)