Marijuana has been frowned upon in the United States since it blew up in the 1960’s. It has been so frowned upon that it is illegal. Research has been done since then on marijuana and it’s effects, short term and long term, and now so much more is known about it.
It is no longer necessarily the fact that it is frowned upon, but it is the fact that people simply have more knowledge that arguments can be made. As of recent, multiple states have legalized marijuana and more are on the way to legalizing it.