Not everything that is permissible is prudent. If you attend, you have no way of knowing if maybe the SSPX priest there was thinking of entering into full communion with the Catholic Church. Your going there helps him confirm him to stay put. Your neighbor may see you there, and they may be leaning towards schism. Your attending there may confirm them that it is ok for them to schism. Your daughter is influenced by the anti-authority American culture. When you defend the anti-Magisterium SSPX, you don’t intend to reinforce her different temptations (that the Church has no right to limit contraception, same sex marriage, etc). But your actions make it more likely she will oppose the Church.
Saying “things are complicated” is another way of justifying procrastination. I hear the same argument from people who justify continued contraception, or divorce/remarriage situation, or who stall getting out of a certain political party or dissenting Call to Action, and other things they should be changing now. When people tell me to lose weight, I tell them “things are complicated now”. The problem with the SSPX is not that it’s too old fashioned, the problem is that it’s too 2014. 100% percent of Catholics have some grievance against the Church. Should we all say “I’m not going to change yet; there are complications”?
There’s huge pressure on people in the SSPX to “stay put, another year, there are other concerns that must be addressed first, there’s this new issue that came up, we’re almost there, the Vatican’s statement leaves question marks, let’s not be hasty, hold the fort, if we surrender now we reward injustice, maybe the next pope, don’t break ranks, wait…wait…wait.” I predict they will be doing this 40 years from now. Individuals should look at the larger impact of “staying put”.