That's not quite how the law works. If I tell you to get off of my property, and you stand on my lawn, you're trespassing, even if I didn't put up a military-grade wall. Or if I have a basic chain link fence, and you climb over it, you're clearly trespassing in situations where without the fence, if you were to incidentally walk across my lawn, you'd be okay.

The point of digital trespass laws is very similar. Just because your technological measures are imperfect (as the bullets say) doesn't authorize you to circumvent them.

What's damaging in this case is that Google created the signalling mechanism, gave it to users, and then intentionally chose to circumvent it.

Courts are also not machines. A lot of this comes down to intent and reasonableness. If you're fingerprinting my browser when I'm in incognito, that feels like an intentional digital trespass which courts would probably recognize. If you're incidentally collecting my IP in your server logs, that feels okay. Programmers get caught up in this all the time -- they read laws and contracts like code (strict literal meaning). Lawyers read them looking at things like impact, intent, whether things are substantially similar, and so on.