- Courthouses come after you would rush HAs, which is the most important "whipped" military unit.
Cuirassers, Cavalry, Cannons are all 100% valid "whipped" military units. So are most medieval units, elephants, and catapults. With AGG Monty has some small bias against HA rushes anyway.
The reason the Sac Altar is good is that it's less

to build, starts good, and stays good. Also, should you get kremlin, the bio farms + fast whip cycle means you can efficiently lollerwhip stuff like tactical nukes back-to-back and not even worry about the

from the whipping. It's silly to say "nope...can't use it with HA...not as good!"
- It also comes after whips on granaries, libraries, and courthouses!
In most cities, you'd rush to whip the sac altar (which IS the courthouse) immediately after the granary. Only early, pre-CH cities would do the library first, and that's where you'd get your first great people. Such is true regardless of civ really; production cities aren't particularly intrested in ASAP library unless you're going for a very late game, since the actual beakers from it in non-

, non GPP cities aren't very impressive.
Courthouses aren't a great building for the early to mid-game. When not organized, it's rare that they're a better investment than building wealth
But the altar requires fewer hammers, making it closer to ORG, and a direct production benefit in most cities, which CH do not.
Late game even if you're running slavery the main limitations aren't happiness but food (and competition from drafting)
If you whip at every opportunity from a city for 20 turns (not unreasonable in a war buildup),

is in fact a limiting factor and you have to pay something to compensate. Not so with Sac Altar.
Drafting is legit competition, assuming you're going the rifle route.
Keep in mind of course that Sac. Altar whips also apply to buildings.