Where there is no resistance Mass a Catholic should stay at home.
One has an obligation to attend a valid, licit and moral mass, under pain of hell, regardless of the priest's views (assuming he's a valid priest). The resistance masses are not the only masses.
This has nothing to do with sedevacantism or liberalism. It is simply catholic moral theology that you cannot attend the Mass of a heretic.
If you're talking about the novus ordo mass, I agree, it's heretical. Outside of this, you're being extreme.
The SSPX are formally aligned with the conciliar church which makes them modernist heretics.
The SSPX is very close to being 'red lighted' in my opinion, but not yet. Sunday masses, by and large, still fulfill one's sunday obligation, even if the sermon is full of propaganda and the church is full of sheeple. Until the sspx formally becomes indult, and outside of marriage masses where the novus ordo "priests" are involved, I would attend if I had to. The obligation to honor God through a valid and pleasing Mass outweighs any ancillary questionable orthodoxy.