[ultima ratio]

"The Society itself preaches this very separation, it is its reason for being."

Untrue. It's reason for being is to adhere to Catholic Tradition. From the Society's view, it never left anything and thus never separated from anything. Rome makes this accusation, not the SSPX. In fact,it has made no changes in its teachings or practices throughout its existence.

[ninenot]

Your argument rests on the assumption that Rome and SSPX HQ are equally valid legislators--similar to the argument of the political Left that the US and Iraq are equal nations.

The argument is flawed because Rome MUST be granted priority by virtue of the presence of the Successor of Peter. SSPX does not have such a person handy. (Similarly, while the US Government acts largely within the universal moral code (natural law,) the Government of Iraq does NOT. Thus the US must be granted priority)

None of this, however, is to malign the motives of those who attend the SSPX Mass.

However, in those locations where there is an Indult Mass AND an SSPX chapel, and the member of the faithful in question suffers equivalent hardships to attend either Mass, and chooses to attend the SSPX Mass---now there is a problem for the one who chooses the SSPX Mass. It can be argued that in that specific case, the individual is choosing to separate from the Pontiff AND those who adhere to the Pontiff.