You know, generally speaking, placing additional burdens on individuals is not a good thing. That's why the Church has certain requirements for Baptism (that the child will be raised Catholic, they have 2 godparents to ensure their spiritual formation, etc.) That's why the Church forbids "stealth" baptisms: going in like a commando, baptizing Jєωιѕн or Protestant children, and getting out of there. Mission accomplished!
More mortal sins is never a good thing. A lower place in Hell is not a good thing. More attacks from the devil is not a good thing. More crises of conscience is not a good thing either.
That's why the Archbishop (who had the mind of the Church) gave the seminarians/priests more time before asking for a perpetual commitment.
But the SSPX isn't primarily concerned about souls -- only secondarily. Their FIRST PRIORITY, their PRIME DIRECTIVE these days is the good of the SSPX: growth, increasing influence, revenue, and numbers, maintaining what they have, etc. If they have to compromise, so be it. If they have to commit serious sins here or there, so be it. If they harm certain souls in the process, so be it.
The SSPX now exists for its own sake, which is ridiculous of course but such is the truth.