It doesn't turn the group masculine, it turns the word used to the masculine plural, which is the generic word for a group of people.

But if you take sciences, for example, it's plural feminine in French and Italian.

If you put a masculine discipline in the group, for example "law" which is masculine in Italian (il diritto), the group of disciplines is still referred to as feminine "le scienze"

It's a matter of gender of the plural word, it has nothing to do with biological sex.

Thanks! Good points. I half wonder if my teacher’s grievance didn’t come from living in a majority anglo culture.

I remember when I realized this learning Spanish that it made me a little sad that I could only ever be part of ellos and not ellas.