This is exactly the kind of representation that the second legislator says is irrelevant to science. It's not a counter, because it doesn't undermine the idea that this type of balance is useless for science.

We don’t care about the individual participants. We need to weaken the second legislator’s claim about male/female balance considerations, which doesn’t deal with individuals.

This explains why research is often done only on male participants, but it doesn't explain why male/female balance considerations may in fact have a place in science.

We’re not interested in scientists' training. We need to know whether the participants’ sex is relevant to research, and this doesn't tell us.

Considerations about male/female balance aren't just for equity reasons, they impact the results of scientific research. This undermines the legislator's claim by giving another reason to care about this balance.