Liberal Gun Owners

that does not prove that I didn't commit the murder.

I agree, but it is evidence that you did not commit the murder.

It proves--probably--that I was across the country at 5pm on Saturday

I don't think you know what "prove" means. "It proves --probably-- " is nonsense, either something is proven or or isn't. Nothing is "probably" proven. It is however common to have evidence that something is probable or not probable.

first, you're saying that civil rights aren't rights at all

All rights have limitations on them:
Free speech/expression: you cannot display your pornography collection on the street outside an elementary school. Right to vote: felons cannot vote, 17 year olds cannot vote
Freedom of movement: private property
Life, Liberty, and the pursuit of happiness: any idiot can purchase a gun, not handle it safely, and shoot you.

There is no civil right that all civilians can take part in any time they want with no restrictions. (This ignores the fact that guns do not need to be a civil right).

secondly, who defines "risk"?

And here you dive into a slippery slope fallacy. Drivers licenses are regulated with restrictions on who can acquire them, somehow no one has tried to deny drivers licenses to minorities or political opponents. Creating a reasonable restriction does not necessitate the creation of unreasonable ones. Each can be taken on a case by case basis.
Is it reasonable to require training before being allowed access to a deadly weapon? "What about LGBT?" What about them? We're talking about training here.