Why this idea that this will "open the flood gates"? They only way that makes sense is if you genuinely believe that being transgender is a decision you can make in the blink of an eye -- not in practice, I mean, but independent of what the law is. Do you believe that a man can wake up one morning and say, "oh wait I'm actually a woman -- time to chop my bits off then and uproot my life and change every single relationship I have right now!" (or vice versa) , without any history to suggest so?
It's belittling, and a nonsense, and an insult to the dilemma anyone who seriously has questions over their gender identity. If anything, this is actually a reason for making the law less tight, because it's enough stress as it is to contemplate telling your parents, who have known you longer than you have known yourself, that they have seen the wrong person all along; to tell your friends that they should see you differently from now on; perhaps, for many people, to tell your partner that you are not the person they married; to tell your children that now you are not their mum anymore but their dad; and to face all the stigma from others this still provokes, day in and day out. On top of that, to have the law often require you to live as your identity without surgery for months or years (so that you may stick out like the proverbial sore thumb, and thus risk exposing yourself to ridicule in day-to-day life); or to have to undergo rigorous testing for what ought at its heart to be a personal matter anyway, is invasive and just adds to the stress for those affected.
I can see the case you are trying to make. This is absolutely not a decision to be made lightly, and the law partly tries to ensure that. But, frankly, transpeople know that well enough already, thank you very much.