I'm in full agreement with the above comments.
The reason I disagree, is that we are not talking about a Commandment of God (Thou Shalt Not Commit Adultery) or the Church (forbidding the eating of meat on Friday), as in the examples given here.
I think this is more a question of a prudential moral judgement. Bishop Williamson says in the interview that in his opinion it is predominantly a pastoral question, not a dogmatic one.
Now don't misunderstand what I am saying. Just because it is a prudential judgement, doesn't mean to say it's therefore okay to do as you please. If it is gravely imprudent to do something, then you sin by doing it. For example, placing Tradition in the hands of neomodernist Rome! However, prudence takes account of circuмstances. That is, circuмstances may alter the prudence or otherwise of a given decision/action.
It is true to say, in general, that it is
very dangerous to attend the New Mass, and to give the
general advice that one should not attend. Just as it is true to say that it is dangerous for men to go to the beach, and to give the general advice to Catholics to stay away from such places, as I explained in my post above. I would go further and say, that today, it is almost always
gravely imprudent to attend the New Mass, for someone who is well informed on the matter.
However, there are
circuмstances relating to the
New Mass and circuмstances relating to the
individual which can change the morality/prudence of attending or not. Not every New Mass is the same. Not every individual is the same. Just as not every beach is the same, and it does not necessarily represent the same danger to every individual, and any given individual may have some other necessity which would make it permissible, even advisable, for him to go to such a place. What Bishop Williamson mentions in this interview is "certain
exceptional circuмstances".
Take again the example I tried to make above. A starving pauper jumps the fence to take an apple from the orchard to keep himself alive. A wealthy prince jumps the fence to take an apple from the orchard to satisfy his love of apples. Exact same action, different circuмstances. The former is virtuous. The latter a sin.