There is a temptation for libertarians to make an illogical leap from “Vices are not crimes” to “Vices are not wrong”, and too many succumb to the temptation.
There are many things one should not do that nevertheless should not be viewed or treated as crimes.
Generally, one shouldn’t lie. It would be wrong to tell your spouse you were working late when you were actually at a strip club or out playing poker. It’s not a crime, but it’s wrong.
Identifying a situation where lying would be justified is quite beside the point; the point is we can identify circumstances where lying is wrong, though not a crime.