It's a bit more complicated. Yes, some words get watered down in their vulgarity or strength of stigma, while others increase.
Sometimes a vulgar word gets replaced by a euphemism, but eventually the euphemism gains more and more stigma as to need euphemizing. In AmE, if one needs to ...well... I'll just pick one... urinate, you go to a particular place. The place where you go to do this is nominally the toilet, but at some point in my older relatives' past, they used to call it the commode (which I had only found out recently is nominally a piece of furniture related to the vanity (a metaphorical metonymy on its own)). But nowadays that place is just simply the bathroom, as in "I have to go to the bathroom", which can be literally true since (in US home architecture anyway) almost all rooms with baths in them also have a toilet, but the phrase -means- 'I have to use the toilet'.
(Without checking the OED, I wouldn't be surprised if 'toilet' is the name of some furniture like 'commode' that has become a euphemism for something one urinates into.)
If a word becomes taboo, people still want to refer to the concept, so they come up with another label for it. As the concept itself (whatever word is attached) still remains, the new label might get similar stigmatization and become taboo itself. I'm sure there's a G. B. Shaw quote that's relevant here but I can't remember it or find it.
Other cultural factors come into play. For example, my grandmother used to refer to the descendants of African slaves in the US as 'colored' or 'Negro', both of which sounded slightly shocking, but quaint and old-fashioned at the same time. To us at the time the accepted term was 'black' (there's a whole literature surrounding that word). But now that is not vulgar, just out of fashion, and nowadays the term is African-American.
So some words lose their strength of taboo, others increase and need to be replaced by one with less strength.
As to the particular word mentioned, 'rape', yes, I've heard of similar phenomena of weakening by repetition in that crowd. But fortunately, I really don't think it is translating to the rest of society. Relatedly, the word 'violate' I think used to mean 'rape' but has itself weakened to just mean 'has been transgressed' (argh..I looked things up...rape -used- to mean the weaker thing, simply violent seizing or carrying off, but has come to mean the even more transgressive sexual violation; but that could also be a cultural thing, that it is now considered more of a transgression now than before).
Words and concepts...so confusing.