What would the ramifications be if they ever found out you lied? It’s an innocent lie, but still, I can imagine that lying on these types of forms could turn out badly.
Revoking naturalization or a green card involves a huge legal effort, but if it can be shown you lied on the application, that’s a much easier case.
Many US laws seem to be designed for ease of prosecution than for strict fairness. For example, open container laws are probably easier to prosecute than drunk driving.
It's not the lie itself, it's that you lied at all. Now you are untrustworthy. Drug use in the past is typically not an issue, particularly if you were young at the time. The whole process is to determine if you have good judgement and can be trusted.
The guidance these days is to tell the whole truth and describe the circumstances. Lying on the form will definitely disqualify you and a couple dumb things a few years ago won't necessarily.