I believe the line the OP was drawing was between regulating how one uses chemicals personally in a manner that does not affect others (directly or indirectly),

I believe the line the OP was drawing was between regulating how one uses chemicals personally in a manner that does not affect others (directly or indirectly), vs. how one uses chemicals generally which may affect others. Note that you can certainly ingest chemicals for completely personal and recreational use and still adversely impact others (e.g. drinking and driving, dosing for athletic performance, neglecting childcare to get high, I had a neighbor get high once and he painted hieroglyphs on the utility box on the street which I didn't particularly care to look at nor feel like spending my time to paint over it - I could care less if he got high and trashed the inside his house asside from property value loss when he sold his home). The examples you site (e.g. burning of gasoline and releasing byproucts into the environment, using dangerous chemicals in consumer products) are all applications that will adversely impact others and should be regulated. Personally, while there are exceptions, I assume people are inherently good and capable of making their own decisions. So, I agree with the OP - if you're not causing any harm to others, I say do what you want.