If a man wants to swim with his artificially created breasts flopping about, whatever. Men come in all shapes and sizes, they're a diverse sex class.
You'd think a bit of sense would dictate he'd make his case better wearing an appropriate swimsuit for someone with breasts of the type he'd like them to be seen as, but it's not in any way helping demonstrate that he and his boundary issues should be let loose in the women's changing rooms or that he should be permitted to go and destroy women's rights to sports of their own.
Edited: no, not make 'his case', there's no case to make. I meant that a man with a trans identity competing with dignity and dressed as he wishes to present himself is going to gain an awful lot more public support. Although not to let him invade women. Just to be himself.