This is not a question of opinion or prudence. It is about fidelity. Archbishop Lefebvre founded the Society to resist the system. To attend priests who have bound themselves to that system is to abandon the very fight for which he gave his life.
If that is the case, you would never have followed the Archbishop before 1988. You would have been a home-aloner way back, perhaps following the Abbe de Nantes from afar? Then where would you be now?...
The Second Vatican Council was from 1962-25. The Society of St Pius X was erected in 1970.
What the Neo-SSPX has done in making deals with modernist Rome is gravely imprudent and will most likely have dire consequences, some of which we are seeing already with the acceptance of doubtful sacraments, including doubtful priests.
But that does not translate into sin or a danger to the Faith for everyone who attends good Catholic SSPX Masses as you want to insist. Such rigidity and lack of pastoral prudence endangers souls in my opinion.
I am not opposed to souls taking the decision that it is best for them or their family not to attend the SSPX, but I am opposed to the view that it must be given the red light for all. I have no doubt that Archbishop Lefebvre would have been of the same mind, as was Bishop Williamson.