taking ecstasy is already illegal
Those who wish to break the rules are not stopped by legislation but by enforcement. That is the reason why this chap provides a good case for random testing. A more proactive CAA might have weeded this guy out of the system and saved two lives but such proactivity would be a hindrance to the majority of PPLs who are rather more sensible.
I don't foresee widespread random testing in GA as I don't expect the CAA, police or anyone else would wish to bear the cost. RAF pilots are routinely randomly tested and I do not know a single one who thinks it unreasonable. Perhaps a hair, blood, or piss-test should be part of the CAA medical.