In both these cases, individuals are talking about broader societal trends. It's not a contradiction if they aren't talking about their own specific experience (i.e. "I'm silenced, therefore I can't talk, listen to me talk about how silenced I am"). An 18th-century writer discussing sex may contribute to the counter-argument that by virtue of their writing about sex, it isn't as taboo a subject as they imply. But in and of itself, it isn't proof that such a trend does not exist.
I didn't really try to make an argument, nor even say I agree with Foucault here--just that I see a parallel and it amuses me.
Caveats: 1) I read this over a year ago, 2) found it enough of a slog that my understanding feels pretty fuzzy, and 3) am still undecided/chewing on the main argument
My impression is that Foucault wasn't trying to deny a trend, but to highlight a number of other trends (including the explosion of discourse around sexuality) to open the reader up to challenging or re-framing their received knowledge about sexuality at the time. His focus is very much on all of the power and control dynamics at this nexus. It's a little hard to distill what I mean by that--because it includes actual sex and sexuality, the science/study of it, who is speaking, whose sex is being spoken about, what kind of sex it is, social/class dynamics, etc.
In both these cases, individuals are talking about broader societal trends. It's not a contradiction if they aren't talking about their own specific experience (i.e. "I'm silenced, therefore I can't talk, listen to me talk about how silenced I am"). An 18th-century writer discussing sex may contribute to the counter-argument that by virtue of their writing about sex, it isn't as taboo a subject as they imply. But in and of itself, it isn't proof that such a trend does not exist.