Exactly right...in my opinion, judicial activism is wilfully ignoring the written Constitution...whether you are following a prior decision that did so...or whether you are doing so for the first time on a particular issue
No, but it its general expression does tend to have the form of "deciding that existing law is wrong and should be overturned."
In that sense, Thomas is indeed leaning toward the "activist" label, whereas Scalia, in his reference to the law as written, is more in line with the "interpret the law, don't make it" position.
We can certainly debate whether or not Congress ought to change marijuana laws. I'd just as soon not let the Supremes do it.