Well, those who attend SSPX chapels, as well as sedevacantists, are both outside the "normal Church structure" -- we don't attend our local parishes.
As St. Athanasius said, "They only have stone buildings. We have the Faith" or something to that effect.
But for me, it's only because attending the local parish would be dangerous to my faith -- which is something to be closely protected and cherished.
I, and most others I know, want firmly to be a member of the Church Christ founded -- and we are. But we must distance ourselves from the error of Modernism (and other errors) and so we sadly watch what is going on in the Church hierarchy (and parish churches) today.
But we have no desire to leave the Church, have never left, and would be the last ones to leave!
When you're willing to undergo scorn for the Faith, you're not exactly the type to leave it! Besides, we're taking the harder road. If someone can lift 800 lbs, I'm sure he can lift 25 lbs. "He that can do what is difficult, can do what is easy."
If I can drive 1/2 hour to Mass once a week, I'm sure it would be easier for me to walk to my local Parish for daily Mass. If that was the better thing to do, you better believe I'd be doing it -- no matter what anyone said or thought of me.
In Christ,
Matthew