Gervase, a question - which of those illegal substances was the first one you used?

The 'gateway'argument is only old hat to those who wish to continue their consumption without the risk of prosecution and therefore shout loudly for its legalisation. There are a great many people who would disagree with you, and whose voices aren't heard because, as it's already illegal, they don't need to shout about it.

You may feel you've got away with your (apparently extreme) substance-abuse scot-free. I'd be interested to hear the views of your family, friends, employers about that. Assuming you still have them.