In a number of ways.
Because men who have surgery to remove their penis often believe it makes them into a woman, thus earning their eligibility for women's rights, spaces and sports.
I realise nullification surgery is a particular subgroup of surgery, but men and society often view people as 'men' and 'non men' - diluting 'women' into 'everyone that the men don't want in their category'. This in turn impacts on women's specific needs as a group and even our ability to describe ourselves.
Many women are also concerned about the safeguarding aspect of these surgeries being pushed on very young patients. I know they're illegal for under 18s in the UK but I still consider 18 to be very young, when you consider we're talking about permanent sterilisation.
If you don't consider yourself trans, you'd be a lucky woman to be allowed to be sterilised before your mid 30s 'just in case you change your mind'. But utter the T word and all caution appears to go out the window. Non trans identidying women aren't generally considered competent to make that decision for themselves.
I'm sure there are more...