Jesus equated it to adultery...hence breaking the commandment.
the 9th commandment, by our numbering, did make the cut—but there is a difference between this and, in Paul’s words, actually joining one’s body to another.
I'll post the words of Christ one more time.
27“You have heard that it was said, ‘YOU SHALL NOT COMMIT ADULTERY’; 28but I say to you that everyone who looks at a woman with lust for her has already committed adultery with her in his heart. Matthew 5:27-28 NASB
You did not merely suggest a majority of Catholics commit adultery—you said that you would wager that every day a majority of Catholics commit adultery.
Wager, suggest....in either case the majority of Roman Catholics, Methodists, Baptists, Presbyterians, etc....commit adultery based on the way Christ defines it.
He equated lusting after a woman to have already committed adultery. It's crystal clear. The thought of sex with a woman is equal to adultery. It's a violation of the commandment.
If you look up Exodus 20:14 and 20:17a you will discover that they are two distinct verses and two distinct but related commandments.
Breaking 20:17a and only 20:17a does a number of things which are bad, but will not, for example, get some one pregnant. It also does not reach the level that Paul is dealing with in I Corinthinans 6:16 et al.
There is a reason that Our Lord included the final clause in the two verses he cited—”IN HIS HEART.” By doing this he closely allies the sixth and the ninth commandment (Our numbering) but he does not say that they are the same—indeed by introducing the two verses with different phrases he makes it quite clear that they are distinct in Moses, but that they both need to be taken seriously.
Before passing judgment on Catholics (or Methodists or any denomination that does not have access to a mind reading device that allows for exercising diligent expulsion of people who have improper sexual thoughts as advocated in post 37), I would note that a thought that a thought observing the sexual nature of another is not automatically lust—if it is not about a spouse, it may be a temptation to lust, but whether or not the person gives in to lust depends on what is done with the initial thought, not upon having such thoughts.
Actual Catholic teaching is really big on custody of eyes and thoughts. It isn’t always lived out, but it isn’t always not lived out. I’d bet that Baptists etc. also have similar teachings and at least some success.