No, they're schismatics.

Firstly, in this thread "home aloner" should be read "dogmatic home aloner" which is someone who is home on Sunday for *dogmatic* reasons -- not accidental reasons like "there doesn't happen to be a Trad chapel in my area". That is NOT how "home aloner" is used in common parlance on CathInfo.

To use the lifeboat analogy --

The original ship (mainstream Church, with associated parish churches visible in every neighborhood) has hit an iceberg, and is sinking. Thousands, maybe 3/4 or more of the passengers, have already drowned (lost the Faith, lost their souls, etc.)

Trads would say, "abandon ship! Into the lifeboats!" and survive until help comes -- only God can solve the Crisis.

Home aloners would indeed jump ship, but refuse to get into any lifeboat, because it's not "legitimate" because they didn't pay the extra fee for "lifeboat service". I know there is no real analogy for it, but basically they think it's not legitimate to attend "illicit" chapels set up by priests who weren't given permission to say the Tridentine Mass. They think the whole Traditional Movement is not allowed or legitimate. So they stay aloof from the Conciliar Church AND the Traditional movement. So Home Aloners stubbornly stay in the ocean by themselves, clinging to a piece of driftwood at best. That is their prudential move.

Where this analogy DOES work so well --

You have 3 options.
1. Stay in the Conciliar sinking ship (where so many have already died, and YOU are likely to die as well)
2. Be stupid and abandon ship without any means to support your life at sea (read: lifeboat)
3. Abandon ship, and make sure to enter one of the many lifeboats available, to preserve your life until help arrives.

Which of the 3 options is the most prudent? I say it's #3. And that's why I'm a Traditional Catholic.

Dogmatic home-alonism is an easy way to despair and lose your faith. It's probably even happened before.

They are, you ecuмenists. Per the reasons Matthew laid out, they refuse to commune with the rest of the faithful. They are, by definition, schismatic.

What if a Catholic believes that the mass offered by the traditionalist priest in his area is illicit and decides not to attend?
At what point did he commit the sin of schism?

To answer your question "At what point does he commit the sin of schism?" --

When he believes he's among the last 2-dozen Catholics on earth, and doesn't attend Masses from any Trad group for dogmatic reasons.
YOU tell ME. Where is the Catholic Church to this potential schismatic? Up and gone, I guess. Completely invisible.

At least Trads have a decent answer, like "the Conciliar Church sort of still is" or the Sedes and others might say, "The Catholic Church remains in the world of Tradition."
But if you boycott BOTH OF THESE? You literally think the Church is a dozen or two laymen, and this for a couple decades without the world ending?

Yeah, I'm thinking Schism AND Heresy.

But one doesn't have to claim that none of the traditional chapel attendees are Catholic to avoid traditionalist chapels. One could refuse to attend masses by traditionalist priests because of some law and then believe the others are simply mistaken and attending in good faith.

Dogmatic home-alonism is an easy way to despair and lose your faith. It's probably even happened before.

Indeed.

Good point.  One does not necessarily have to hold that they are not Catholic in order to find reasons to avoid going to Trad chapels.

First of all, I need to add the word "all" to "Trad chapels". Because again, we're not talking about someone who lives in a Trad wasteland area with only 0-1 Trad options. I'm talking about people who reject the Traditional Movement AS SUCH because it's not legitimate, no jurisdiction, etc. As in, the solution to the Crisis in the Church is to Stay Home -- for 52 years and counting. THAT is what these "dogmatic home aloners" believe.

What are these "reasons" which dispense one from communion with perfectly good Catholics, to say nothing of meeting one's Sunday obligation?