Agree to disagree.

A GSA gives students a support network, and a sympathetic peer group.  It shows them they are not alone, that the school system - which their lives revolve around at that age, is supportive and understanding.

A support and understanding that they may not receive at home.

I live in Richmond, which has many parental groups who are very vociferous about no gender neutral washrooms, no sex education, and no  GSA groups in schools. 

In fact the last provincial election "anonymous" flyers went out warning voters not to vote NDP because of their more liberal stance on these issues.

http://vancouversun.com/news/local-news/richmond-chinese-election-ads-slam-moral-destruction-in-east-vancouver

A safe haven school based GSA, until kids grow into adults, with more strength and resilience.  What is the harm in that.