Why did the us move away from the gold standard. couldn't they just change the value of gold if they wanted to raise or devalue the dollar?

Imagine instead that angel raich and diane monson were arrested at a pro-medical marijuana rally they had organized in a public park in california and faced several charges: 1. violating a public decency statute because they were wearing t-shirts that read "ignore the feds, weed is not a crime! " with pictures of marijuana leaves surrounded by flames and guns, and 2. violating a town regulation that prohibited being in the park after sunset. raich and monson argue that both charges should be dropped because their actions were protected by the first amendment. 1. what is raich and monson's argument that they should be allowed to wear their t shirts 2. what is raich and monson's argument that they should be allowed to organize a rally in a public park? 3. what is the weakness is raich and monson's argument about the rally?