You're missing the most important part of that conservative principle, freedom comes with responsibility, and the responsibility here is NOT putting others in danger by exercising that freedom while driving and thereby putting uninvolved innocents in danger.
I have no problems with people smoking some or honestly doing any drugs they choose, as long as they deal with the responsibilities of those actions, not driving, any health issues that arise due to their uses, financial issues, etc.
Your freedom to be you includes my freedom to be free from you and the repercussions of your choices. When you decide your freedom Trump's mine, we have a problem, and I'll act to balance the scales.





