Again, this is where I think it depends ENTIRELY on how broadly the law is written.
If a law is written in terms of anti-discrimination that spells out that "gender identity" or "transgenderism" relates specifically to those who have been clinically diagnosed and are undergoing, or have completely undergoing, active steps to transition their gender then I think the potential for fraud is ridiculously small and thus easy to overlook as a troubling aspect.
However, when the law is written in extremely broad fashion, with little true definition of what serves as "gender identity" or "gender expression", with no guidelines on the length that such things must be occurring, what manner or burden of proof is required, etc...then I think the potential for fraud is far broader and is at least worthy of looking at, while not necessarily serving as a defacto automatic "shut down" of a conversation.
Take for instance handicapped parking as an example here....
There are clear designators for our cars as to whether the individual is handicapped. There is clear codified methods to determine if and when someone should be given such identification and status. While there are broad ways of being designated handicapped, there is specific guidelines or requirements to be identified within those broad categories. And in all those instance, it is requiring a professional 3rd party opinion to make that determination. While there is still "fraud" that occurs, both in terms of people fraudulently using identification wrongfully or just ignoring the need for identification all together, overall because of the system in place such fraud is limited and relatively easily identifiable and combatted.
However, if the law basically stated that if you feel like you're handicapped, then you're handicapped, and you must be treated as such...then the potential for fraud would expand greatly. Suddenly an overweight person could simply feel like they're "handicapped" and shouldn't have to walk as far in a parking lot, so they park there. Suddenly a person who woke up with a sore knee could decide to park there. Or suddenly someone looking to get one over on the system could park there simply because it's closer, and then just put on a little bit of a limp or even just claim they have a handicap that is not outwardly noticeable, because they knew there'd be no real way to prove them wrong easily and thus it'd be highly unlikely there'd be any negative to do it.
Clearly defined parameters and methods for making determinations of these things, outside of ones personal FEELINGS, is necessary with these kind of things.