True, marijuana is NOT classed as adult oriented material - and a site like this can be classed as an informational site, like Erowid and the like.
Try putting a disclaimer at the bottom stating 'This site and all writing pertained on it is for informational purposes only, I do not condone illegal use of marijuana' yadda yadda waffle waffle...
And if they still tell you to feck off, see a solicitor about it.