In one sense, schism can be a "social sin" if the acts of the schismatic are shared communally. In another sense, it could only be internal and/or expressed externally by removing oneself from all other Catholics and refusing communion with them or say secretly hating the pope and refusing submission to him in spiritual matters. Do you agree with this?
As previously mentioned, receiving Sacraments from a schismatic group might render one "suspect" of schism, but it's not necessarily objectively the case ... and ESPECIALLY since the groups we're talking about here haven't even been authoritatively declared to be in schism. You keep speaking of this as if a declared schismatic group like the Orthodox are in the same category as various groups Trads have "declared" to be in schism. Even IF it were a declared group, it's not certain ... but then in the case of a group who has not been declared and the assessment is based merely on your own private judgement, there's not a chance that merely assisting at those Masses would constitute schism of any kind.
So your premise seem to be not only that declared (and professed) schismatic groups are in the same category as groups that profess to be Catholic and about whom the Church has not authoritatively determined otherwise. That's apples and oranges. Not only that, but then you're implying that this putative schism (based on your private judgment) is even somehow contagious or communicable. So, if someone whom you do not consider to hold schismatic positions attends a chapel of a group that does in your opinion hold to schismatic opinions, even though he himself does not adhere to the schismatic posiiton, but has merely judged it licit to attend the chapel (for reasons, say, such as those I articulated) ... now that person is schismatic not for actually holding the schismatic opinion but merely for holding that it's OK to go there for Mass since the Church hasn't been declared schismatic. Or, as some groups do, you hold a position to be heretical, so that even if I don't hold that heretical position, I'm a heretic for just disagreeing with you that it's heresy? In other words, I don't agree with the alleged heresy, but you judge me a heretic for disagreeing with your assessment of the theological note.
These dogmatic types of opinions and positions are in fact the primary tendency to schism among the majority of Traditional Catholics, i.e THIS thinking is precisely the closest thintg to schism, where ironically it's those who declare many/most other Trads to be guilty of schism that are actually most in danger of being schismatics themselves.
Here's an example. You hold that the CMRI are schismatic. I have nothing to do with the CMRI and disagree with many of their positions. But I disagree with your judgment that the CMRI are schismatic. Therefore, you delcare that I'm a schismatic for not considering the CMRI to be schismatic, even though I actually have no connection whatsoever to their group or their attitudes or whatever you consider problematic about them. Where does it end? If I'm CMRI, I'm schismatic? If I don't think the CMRI are schismatic, I'm schismatic? If I don't think that someone who doesn't think the CMRI are schismatic is schismatic, then I am schismatic?
ad infinitum et ad absurdum