The use of marijuana or other narcotics has been discussed by every single moral theologian, and they all gave the same answer, namely that the sinfulness of its use is the same as for that of alcohol.
There is not one single moral theologian that anyone has produced here who said that all recreational use of non-alcohol drugs is always mortally sinful. People have quoted Jone and Prummer, but they are only giving the consensus opinion. NO ONE on the other side has produced a single pre-Vatican II theology book that says all usage of marijuana is sinful. I would really like to see such a quote if it exists, though I'm fairly certain it doesn't.
As Catholics we are supposed to learn what is right and wrong from theologians, not our own opinions.
Every action is presumed to be licit unless the contrary is proved. People asking for a Catholic source saying that using marijuana is okay are making the wrong argument.
No simple priest, SSPX or otherwise, has any right to say that the unanimous opinion of theologians is wrong in allowing the recreational use of drugs if it does not impair the use of reason.