Huh? No it isn't. Not even close.
As for why it's been illegal you should read up on it. In a nutshell, it was made illegal in the 30s because it was perceived as the drug of Blacks and Hispanics. The worry was white kids would start using. That's where Reefer Madness came from.
But then in the 60's marijuana laws were a convenient cudgel against anti-war types. You can't jail someone for protesting but you can jail them for pot.
That's why pot has been illegal in America.