Wonderful question. Really. I just have two things which will make it more effective:
1. The preferred term is 'intersex' now. I know, but using the word everyone else is using makes people less likely to get angry.
2. Transsexual people are a broader category of people who will be impacted by what you bring up. The number of people who are born with an indeterminate sex (intersexed, that is) is a lot smaller than people with gender dysphoria, or feeling like they've been born into a body of the wrong sex. Trans people are still a minority, but they're a larger minority, and a more vocal one, so people are more likely to care about them. It's not the way things should work, but it's the way they do work.