It is fair to say that the meaning of a poem resides in the mind of the reader - certainly some theorists such as Barthes have claimed that. All the same, this poem, regardless of the political history of the poet, is widely held to be about the importance of not allowing the 'creep' of intolerance and totalitarianism, as 'they' will pick off resisters one group at a time.
So if we don't speak out when we first see women called 'cervix havers', it gets harder when we realise that we are no longer mothers but 'birth givers'.
Then the TRAs get women sacked from their careers for saying that it is not possible to change sex, so more people stay quiet and don't speak out.
Then children are taught that there are 101 genders in school, but parents who speak out are called transphobic and ridiculed ('amusing', or 'pathetic' or worse), so they stay quiet.
Then children who don't conform to stereotypes are told they are in the wrong body, and some are given hormones, and by now it is more difficult to speak out as more agencies are involved.
Then we have to declare pronouns on our emails and screens.
Then men are allowed into so many spaces that some women are unable to attend for religious reasons.
Then women are attacked outside of cinemas showing feminist films, or on marches that don't comply with the TWAW mantra.
Then more, then more, then the law is changed so that it is a criminal offence to say that men cannot be women, however much they hate being told no.
Who is left to speak for women then? (luckily, JKR is speaking for us)
Of course Pastor Neimoller wasn't talking about trans issues when he wrote the poem, but to suggest that that matters is missing the point entirely, as is the existence of trans people in 30s Berlin.