==If you are gushing about your kids no one is going to open up about a taboo subject like that.==

This is true. Likewise, if you are explaining all the reasons you can't or don't want to have kids someone may be more likely to agree by saying "I wish I didn't have kids."

I don't disagree with what you have said, just know that taking care of your siblings is not the same as being the parent of a child (legally, emotionally, physically, etc.). When you compare them, it detracts from the broader point you have made.