To be clear, when I say "occasionally" here I'm talking about attendance for non worship purposes, passively attending for a wedding or funeral or what have you.  I definitely agree that if you thought it was an appropriate place to worship, you'd for all intents and purposes fall under the Indult label.

I think ultimately the issue doesn't predominately come down to liberalization pre Vatican II, Sede vs non sede, or most of the other things that people are making this about.

I think it ultimately comes down to whether the NO is a Satanic parody of Christ's sacrifice vs if its simply a Protestantized service.

*Perhaps I am ignorant on some level.*  I was never an NO Catholic. But from everything I'm aware, the changes were *predominately* designed to make the Mass look more like Cramner's Mass.  You've got the communion in the hand, you've got the table replacing the altar, versus populum, deemphasis at least in many cases on the sacrificial character of the mass, etc.  Oftentimes cheesy music.  Honestly things that remind me of my time in Protestantism.  Given that assumption i think the same principles regarding attendance would apply for a Protestant service.  I think you could go for a wedding, but you wouldn't commune there.

However, some here seem to think that its more of a Satanic blasphemy than equivalent to a Protestant service.  If that's the case than I'm ignorant, but also if that's the case I'd agree with not attending, not even for a wedding or funeral.  I couldn't in good conscience "passively attend" a black mass, and I'm not aware of the church ever allowing that (as it has allowed passively attending Protestant churches.)

If its inherently evil to go, then you shouldn't go.  The issue is whether the thing itself is a Satanic blasphemy that needs to be avoided at any and all costs (like a black mass) or if its more like a Protestant service (the thing itself is wrong but the Church lets you go for certain social reasons.)

This is ultimately what the debate comes down to IMO.  

I forgot to add that the difference between an actual black mass and a protestant/NO service is that the black mass is overt worship offered to satan whereas the protestant/NO purports to be worship of God.

I see it as totally equivalent to a Protestant "Mass" and no argument I've heard so far has convinced me at all otherwise, but I'd also be interested in why people think it's on another level of evil entirely.

It seems like emotion to me, but the best sense I can make of the underlying logic is that some people really do think it's more like a black mass.

It seems like emotion to me, but the best sense I can make of the underlying logic is that some people really do think it's more like a black mass.

I think the intention of those at a black mass are entirely different from most in attendance at the NO.

Any trad priest of any background will give the same answer on this, since it is exactly the answer given in any book of moral theology. A person can attend a non-Catholic wedding or funeral if necessary for social purposes, i.e. if the person getting married/buried is a family member or friend. While attending such a ceremony, someone must not participate actively in the religious activities, but only remain passive, such as by sitting through the whole thing in the back of the church.
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A Novus Ordo service is a non-Catholic ceremony, and thus comes under the above rule.
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Anyone saying the Novus Ordo is some exception, such that it would still be a sin even to be passively present and not participating at a wedding or funeral, is incorrect and should be ignored.
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You don't have to trust me on this. You can ask any trad priest you want and you'll hear the same thing.

Both are still a blasphemy.  Both are a fake sacrifice.  Both are anti-catholic.  Etc etc
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If you read +Ottaviani’s rebuke of the new mass (which is just a summary of problems), you’ll see why he called it anti-Trent.  This is proof enough that it’s offensive to God in a great way.  
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+Ottaviani’s study is free online.

Ottaviani is one of the theologians whose books I'd push -- he's classic Traditional Catholic. The earliest Traditional Catholics were all familiar with the Ottaviani Intervention, and it formed part of the foundation or justification for the whole Traditional Movement.

Both are still a blasphemy.  Both are a fake sacrifice.  Both are anti-catholic.  Etc etc
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If you read +Ottaviani’s rebuke of the new mass (which is just a summary of problems), you’ll see why he called it anti-Trent.  This is proof enough that it’s offensive to God in a great way.  
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+Ottaviani’s study is free online.

Exactly. A Protestant fake-Mass is a Satanic parody of the Mass just like the NO. So why was it not a sin to attend a Protestant wedding pre-V2 but it's a mortal sin to attend an NO wedding?

Exactly. A Protestant fake-Mass is a Satanic parody of the Mass just like the NO. So why was it not a sin to attend a Protestant wedding pre-V2 but it's a mortal sin to attend an NO wedding?

If you are comparing simply the NO wedding with a Protestant wedding, you are correct.  The difference, which you fail to recognize, is that if the NO wedding also includes a new mass, that is the clinching factor that you cannot attend.
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It's shocking to me that so many of you have no principles on why we avoid the new mass 100%.  That is part of being a Traditional Catholic.  If you have some exceptions in mind on why it's ok to attend *sometimes*, then your refusal to attend it is not based on doctrine/theology, but pure sentimentality ("it's not as good", "it's inferior", etc).
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Again, if you understood what the True Mass is, how holy it is, how perfect in God's eyes it is, then ANYTHING which makes it less holy or less perfect is an ABOMINATION.  Let's not forget that God despised Cain's offering, simply because Cain made it with a "not as good" intention.
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God is perfect and all-holy.  Thus, the Mass we offer to Him MUST be perfect and all-holy.  This is what He deserves, as Our Creator.  If we give scandal by "passively" attending a NO, we sin by 2 of nine ways of being an accessory to sin - silence and consent.  Thus, we give scandal to everyone else there.  
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It waters down the whole Trad movement if we give into the new mass, because then we send the message that Traditionalism is simply a "preference".  If you can go for weddings/funerals, why can't you go for other special occasions, like Christmas, Easter and New Years?  It's a slippery slope of bad logic, poor theology and a betrayal of doctrine.