Actually, there’s no real consensus as to why “bloody” became a curse word in the UK. The OED cites it from 1695 in that sense, which would seem to be a bit late to be referring to Christ – most of the epithets showing that type of blasphemy (God’s blood --> 's blood) are much older.
The OED says this about the origin:
As Bill Bryson said, it’s like people just suddenly decided that “bloody” would be a bad word. There are other examples of something like this, my favorite being “occupying,” which vanished for a time from the language for its sexual connotations.
The action of having sexual intercourse or relations; use or employment for sexual gratification; an act of sexual intercourse. – from the OED
As far as the use of “poop” instead of “shit,” the former is a euphemism, allowing people to talk about the subject without offense. Sometimes it is necessary to discuss things that are taboo, and euphemisms are coined to make it easier. Euphemisms do change over time, of course: my favorite example is the flipflopping of “arse” and “ass.” “Arse” was so offensive, that the word “ass” was used as a way to say the same thing in polite society. Now, “ass” is by far more offensive, and “arse” is a humorous euphemism.
In the Turkic language family, there are two verbal roots meaning ‘to do’: et- and qil-. In any particular Turkic language, only one of these is used with the meaning ‘to do’. The other is avoided because it becomes associated with sex. Even though it had originated as a euphemism to avoid actually talking about sex.
The 11th-century Turkic lexicographer Mahmud of Kashgar wrote: “The Oghuz use etti for anything that they do, while the Turks say qildi for ‘make, do’, except that this word is in current use for ‘copulation’, so they avoid it in front of one another, so as not to embarrass the ladies by using it.”
(Divan Lughat al-Turk I:171)
This has persisted into modern languages, e.g. in Turkish (descended from Oghuz), they still say et- instead of kil. In Uzbek, descended from the Central Asian Turkic that Mahmud spoke, it’s the other way around, they only say qil-.
Mahmud also wrote: “One says er qizigh qildi, ‘the man copulated with the girl’; this is an allusive phrase for copulation, and the Oghuz therefore avoid the use of this word, and substitute etti, literally ‘to put in order’ for qildi; for example, they say er yükünch etti ‘the man prayed’, while the Turks say qildi.”
(*DLT II:25)
Compare in English slang where “to do somebody” can mean to have sex with them.
So no matter which of the two “do” verbs a Turkic language used, the other one was bound to get an indecent reputation, because obviously people constantly have sex on the mind but don’t want to admit it. A case study of how dirty-word status gets established.
It was a joke. Of course words have power. See the part about not using curse words out respect?
And I would argue that racial slurs are not by definition of this thread “curse words”. Using that logic yelling ‘Fire!’ in a crowded movie house would be cursing.
