Secret identities worked to keep others safe, supposedly. If Superman was revealed, baddies would be kidnapping Lois every week.
Except that doesn't work given that Superman hangs around with Lois, Jimmy, etc. as much as Clark does. It only makes sense if the superhero never interacts with the same people as the civilian identity, which usually doesn't happen because of the economies of storytelling. Lois would get kidnapped anyway, and tortured on the grounds that she
might know Superman's identity. So keeping her in the dark only protects Superman, not her.
In general, superheroes
should let their loved ones know so they can protect themselves. Keeping people ignorant never makes them safer.
And also.... the rise of mobile phones rendered the phone-booth obsolete,
where can a hero change clothes these days?
The weird thing is, Superman never actually changed in a phone booth in the comics
except as a joke scene to poke fun at the somehow pre-existing cliche of Superman changing in a phone booth. It's one of those "Elementary, my dear Watson" things that comes from popular perceptions of the work rather than from the work itself. The one time he really did that was in one of the first couple of Fleischer cartoons, so that's probably where the meme came from.
And also often here illegally.
Not as an adult, since the statute of limitations would've long, long since expired. And if he weren't discovered to be a non-native before the statute ran out (or something like that), he could legally claim to be a native. Besides, illegal entry is only a misdemeanor, despite how it's currently being treated by the government.
For that matter, national territory is considered to include its airspace up to the edge of the atmosphere, so if Kal-El's capsule came in at a steep enough angle, then it might not have actually crossed any legally recognized borders between the US and another country.