I don't think that people should have to go on hormones for a set amount of time of have surgery before they change their gender marker, because as some other people have already said, no everyone wants to go on hormones/have surgery, and not everyone can safely. I think that maybe you should have to do a certain amount of time living as your gender if we're going to regulate it, and nothing else. Maybe even have an intermediate step while you're living as your gender and waiting to be allowed to change it, like the 'X' that some countries allow you to have in your passport to accommodate for people outside of the binary. People who want to go into bathrooms to assault or perv on people are going to find that very hard to do, just like we find it hard to live as our assigned sex, particularly if you haven't been brought up and socialised in that way for many years like a lot of us have been before we transition.
In any case, I think it's a void argument, because I pass as male to pretty much everyone who hasn't been introduced to me as female, and due to not knowing if I'll walk into someone that knows me as female, I don't use male bathrooms. I can think of only a handful of occasions where someone has said anything about me being in female bathrooms, and although I do feel safer having ID in my pocket which states that I'm female when I'm in those bathrooms just in case, no one has ever asked me to "prove" my gender. If a sex offender goes in there no one is going to have the guts to ask whether they should be in there most of the time, even if they don't look like they should be there.
And why anyone thinks that they would be able to see something in a bathroom beats me, cubicles have doors, and anyone would get called out if they were seen looking underneath a door or over the top, regardless of their gender. And at urinals if someone catches you trying to peek at them everyone expects something to go down anyway. Even the whole idea of gendered toilets is based on the fact that everyone must be heterosexual, because homosexual people aren't questioned when they use the bathroom of their sex, and they could be there to perv on people much easier than someone who was heterosexual and trying to get into the bathrooms of the opposite gender. It's probably a lot easier to sexually assault someone in a secluded place than in a toilet, where there's a high chance of someone else coming in and catching you in the act.
As for people trying to use it for terrorism, I'm not too sure I under stand the point that's trying to be made. Changing your name and moving location would be a much less conspicuous way of losing your past identity because then you're going to blend in with all of the cis people, unless you already pass. In Britain it's very easy to change your name compared to most other countries and we don't have an influx of terrorists sneaking around under other names than what they were born as.
Personally I think gender markers should just be scrapped, because the majority of names are gendered anyway, so their ID is going to reveal what gender they are anyway. I know some names are androgynous, but there's honestly not that many people who both have a completely androgynous name, and even less who are are heterosexual perverts, and have the inclination to try their luck in a bathroom.
