You just don't get it, and that's the saddest part. You're
almost there though.
(A) Intentionally not disclosing prior drug use (because you were afraid it would disqualify you for a job where drug enforcement in involved).
(B) Intentionally not disclosing a trip to China (or Iran, or Pakistan, or Syria, or Russia, etc.) for a job that requires US security clearance.
(A) and (B) are exactly the same. Like I said several posts back, It's not what you left off, it's not whether it is drug use, a drug misdemeanor, a trip to visit family in China, a business trip, the 2008 Olympics, or a trip to Canada, or that for four months you lived with a now ex-girlfriend.
Get this through your head:
It isn't the prior act. It is that you lied about it, and they caught you (because you told them). Honestly, how were they even going to find out about recreational drug use? At least with a trip to China while trying to get a job that requires US clearance, they can actually look up customs records, or off your passport.
A person who manges to do that, whatever the omission is, doesn't just suddenly appear like they
might not be trusted, they just
proved that they can't be trusted. I don't know how you can't see the obvious parallel.