Marijuana is "legal" only in 14 states of the US and only for medical use (the use of the word legal is tentative as it does contradict the federal law that's in standing currently). As for WHY this...
All of the STATES in the US can legalize it if they want, to whatever extent they choose. The United States of America IS, and WILL ALWAYS BE a CONSTITUTIONAL REPUBLIC. Not a FEDERALIST SOCIETY.
well the justification for making it illegal is the "gateway theory" which assumes that use of marijuana will lead to use of other drugs. if you made marijuana a legal drug, you wouldn't have to be...