The "sterilizing children" is how anti-trans activists talk about giving trans children gender-affirming care. Framing it this way makes it sound monstrous rather than an unfortunate side-effect of a medically necessary procedure, in the same way that characterizing a surgeon who performs hysterectomies for women with ovarian cancer as "a doctor who goes around sterilizing women" would be painting them in an unfair light.

And of course he's not directly accusing his coworkers of "sterilizing children", but he's 1) using language that compares politically sensitive health services that many of his coworkers or their families may have used and/or may feel defensive about to atrocities and 2) accusing his coworkers of supporting atrocities. That feels quite disruptive and inappropriate in the work environment IMO.