That's not entirely true.  So, for instance, theologians commonly hold that it is acceptable for certain reasons to ATTEND Protestant, heretical, schismatic services ... by way of a PASSIVE attendance, say, at a funeral.  So it's not necessarily true that one cannot "attend" a service that displeases God.  Consequently, the issue is with active participation.

Passive attendance at a Protestant funeral is tolerated, but not even the Church says you can do it for "spiritual benefit", which is what you're arguing here concerning the Novus Ordo.

A protestant service is not sacrilegious.  The Novus Ordo Mass is.

Does not a schismatic Orthodox liturgy also offend God?  Many Church Fathers taught that it does.  So why did St. Pius X allow reception of Holy Communion from such services that offend God?

Again, you conflate a legitimate liturgy which, if said by a Catholic priest, would be wholly acceptable, with a defective, sacrilegious liturgy.  

Please make the case for why it's OK in one type of offense against God (schismatic liturgy) vs. another type of offense against God (offensive ritual as in the Novus Ordo).  I'm honestly open to your making a case, but as of right now I don't see it.  In fact, the context of corrupted schism and heresy would be more offensive to God per se than the presence of an altar girl, for instance.

Let's say I'm convinced that the NOM consecration is valid.  What if I were to ask a priest to give me Holy Communion out of the tabernacle without actually attending Mass?  That's not a formal participation in the offense (i.e. the evil), but rather a material one at best.  Now, what if I do that while passively attending a Novus Ordo Mass that I consider to be offensive to God.  Any difference, when you combine the principle of passive attendance with a merely material participation?  And the rules for material participation in evil then apply.

In the case of the NOM, it would be sinful to FORMALLY participate in the evil by actively participating.  But what if someone were to just kneel there, say, praying the Rosary, and then go up to receive Communion?  It's much more gray in that kind of situation.  By Canon Law, the faithful have a right to the Sacraments, for the good of their souls.  And with regard to faith, the Novus Ordo is in a sense LESS offensive than an Orthodox liturgy, since they at least PROFESS to be Catholic rather than explicitly schismatic.

A schismatic liturgy such as that of the Greek Orthodox, is not heretical, schismatic, defective, etc., in itself, to the point that if a Catholic priest were to celebrate it, it would be perfectly acceptable.

Even a protestant liturgy, silly and vapid as it is, is not necessarily itself sacrilegious.  

The Novus Ordo, on the other hand is, in itself and its theology, objectively sacrilegious.  It (the prayers, ritual, theology, etc.,) is in open opposition to numerous Catholic doctrines touching upon the nature of the Mass, sacrifice, etc (e.g., Session XXII of the Council of Trent, etc.).  I hope I don't need to go into extensive detail on that.  The problems with the Novus Ordo are known to many on this board.

Furthermore, this rite claims to be a true Sacrifice, it claims to be Catholic, it claims to be many things of which it is not.  It claims to be a Catholic rite, celebrated by a Catholic Priest, yet in its theology, prayers, omissions, additions, etc., are objectively not Catholic.  It is celebrated by an individual who is a representative of the Church, an alter Christus, in the name of the Church, but which promotes an heretical understanding of sacrifice, is in violation of a number of principles set out by the Council of Trent, that has its basis in an entirely new theology concerning the Mass, etc.  

It is precisely because it claims to be these things that we cannot go.  In the same way that if I were to simply hold protestant worship service, it would be sinful and silly, but could not really be considered sacrilegious.  If, on the other hand, I were to engage in similar activity, yet claim it was in fact a Catholic Mass, it would become a parody of the real thing, and for that reason, would be sacrilegious.  It would be even more so if I were a valid priest, and even moreso if it were a valid consecration.

Catholic attendance at an objectively sacrilegious activity, what amounts to a parody of the Catholic Mass, particularly because it is a public act of worship, is an entirely different animal than mere presence at a protestant service.

I would be interested, Ladislaus, in you explaining how one can be said to "passively attend" the Novus Ordo yet, when it comes time for communion, to go up and receive, and it still be merely "passive participation".

Now that I consider there to be positive doubt regarding the validity of the NOM, it would be sinful.

Here’s the other thing, Lad.  If you find there to be positive doubt, then there is, and this positive doubt applies to everyone, because positive doubts are based on facts.  Person A, who has studied the matter, finds positive doubt.  Person B, who asks Person A for advice has to be told “Yes, there is positive doubt.”  Not, “Go find out for yourself.”  You can’t have the mindset, “It’s doubtful for me but maybe not for you.”  That’s relativism.  

Not saying you believe that, but it came across that way.  

I question the notion of seeking spiritual benefit at even the risk of offending God.  No matter how you look at it, it's disordered.

Throughout all of the in-favor-of arguments here, the focus is on self rather than God.  I want communion, I want this or that spiritual benefit.  I..., me..., my..., etc.

Were we to focus exclusively on God, on His Rights, on His Will, on His Law, His Honor, etc., any spiritual benefit we would miss out on by sacrificing our own will for the sake of God would be more than compensated for.