Today is Friday.   Ask them if they would laugh, dance and clap when Jesus was crucified on the Cross.
This is why it is called the Holy Sacrifice of the Mass.  

That's a good point regarding the mass, but they still do those things in like vigils and other things which aren't mass.

So what would you say for anything that isn't the mass?

That is antiquarianism. Rolling back the clock to a historical time period (or, in this case, a historical figure) and/or making up liturgy out of thin air (totally breaking with whatever came before it) as an "homage" to that time period/person.

Catholicism is Traditional. It is handed down over the ages, starting with the Apostles who knew Our Lord personally. There must be some reason that before 1970, you *never* had such clapping and dancing in the context of worship. Our forebears in the Faith must have had a good reason for that, which they received from the Apostles and Our Lord Himself. We should respect the Church's Tradition and not do what "seems OK" to our ignorant brains.

But besides the condemned heresy of Antiquarianism, it is also CHERRY PICKING elements of the Old Testament which helps them conform to the modern world's sensibilities.

King David was an Israelite who lived in the Old Testament, under the Mosaic dispensation.

I notice that the Conciliar Catholics like doing things that are "fun" and happy, but I don't see them quite as anxious to roll back the clock to the Mosaic prohibition on pork, or other elements under the law of Moses. They like their bacon and sausages too much for that.

I think everyone can see that the tendency in the modern world is for religion -- at least Christianity -- to be ENTERTAINMENT (bubble machines, lights, stages, audio equipment, a show, no guilt, have fun, perform music, etc.) So this emulation of "David's dancing" is obviously calculated to make friends (rather than enemies) with the modern world and its ways. Typical Vatican II.

So you see, some things help their agenda (which is to fit in with the modern world) and other things don't. That pretty much determines which historical practices they want to roll back to.

The Israelites were also pretty strict about not intermarrying with other races. I don't see the Conciliar religion jumping on that bandwagon. *grin* Again, that is because it would only make enemies with the modern world.