Is there a study that quantifies how many people use cocaine before any other substances?
And without legalizing cocaine and heroin, there will still be illicit drug trade.
Even with legal alcohol sales, there are still home distillers who face tax revenuers.
The gateway claim is nonsense - research shows that the correlation between earlier marijuana use and later use of other drugs can be explained by a "common-factor" model, that is, a third factor that causes both results, such as individuals' opportunities and unique propensities to use drugs, or more broadly a social or psychological predisposition towards anti-social behavior. (http://www.rand.org/pubs/research_briefs/RB6010/index1.html, http://rds.homeoffice.gov.uk/rds/pdfs2/hors253.pdf)
Also note that the same sort of correlation between earlier marijuana and later harder drugs also exists between earlier alcohol and tobacco and later illegal drugs - so if marijuana is a "gateway" so are alcohol and tobacco.
And without legalizing cocaine and heroin, there will still be illicit drug trade.
But quite a lot less - which would be a good thing.
Even with legal alcohol sales, there are still home distillers who face tax revenuers.
How many? Are they anywhere near the problem that the illegal marijuana trade is?