As someone married to a trans man who has been on HRT long enough to pass in rural southern US, I can tell you from firsthand experience that we still are advised to wear protection.

Because, you know, he’s not sterile. (He wishes he was, though.)

Bottom surgery does sterilize for obvious reasons, but like you said, it’s not a surgery often given to children.

There are many medications with dangerous long-term risks associated with them. Among them is birth control, for example.

Unlike birth control, people take HRT being fully informed what effects are associated with the process. It isn’t administered without acknowledgement of that information. It isn’t given unless you are deemed confident in your decision by mental health professionals. And even then, in many places, it often takes years to begin the process.

The “sterilization” argument is a weak one made to alienate and fearmonger. People who truly have gender dysphoria and truly wish to resolve that issue through transitioning would, for the most part, love to be sterile. The thought of using what they were born with in that manner, usually, is horrifying and disgusting beyond belief.

Anyway, I know you’re not the one making that argument. Just sharing my experiences being around it since it’s relevant.