Well firstly, it's a way of stating objections the US has to certain people entering their country. That makes a legal basis. It's their way of saying to every person, upfront "if you do this, we don't want you here".
To most of us, that makes no difference, but those who say, have committed genocide or have communicable diseases are made aware of it. It's a small thing, but it becomes important later. Obviously, someone COULD lie, but that will be big later on. See why soon...
Secondly, IF you commit a crime, and it's at all dubious in court - let's say they think you tried to commit mass murder, but can't make the case. They don't want you around, because, frankly, they know you want to kill, but can't prove it. But now with some CIA research they've found you caused problems in some random African country and therefore lied on your form, booyah, they have a legal reason to chuck you out the country. The punishment for lying to a US official (police officer, border guard, any) can be more serious than the punishment for the crime!
Thirdly, let's say you're a retired spy for ... The Netherlands. Stuff has come out - declassified, and the CIA knows that you were a spy, but hey, you're on good terms. However, you'll need to tick yes for that form, even though everything you've done is legit. It will raise an issue, and it allows US Embassies and consulates to consider the difficult issues like this before travel, when applying for visas.
You also may have been deported from a country, like a Cuban refugee, say. Now, years later, you're all legit, are a politician, but you're going to have to tick yes, because frankly they want to know if someone they deported is trying to get back in, OR more importantly, they may have you on file already. By declaring yes when applying for your visa, the Embassy can sort out this issue before travel, as the US will tell them that it could be a problem, so the proper authentication could be issued.
Consider Nelson Mandela. In Apartheid-era South Africa, he WAS considered a terrorist. He was in prison for decades. Then he became President. So when his office is filling out the forms, you can guarantee the US knew about his criminal past - it was world news! However as President of South Africa, he now had a very valid reason to travel to the USA.
So yes, there's definite value in these questions. It's 'amusing' and 'odd' to think about ticking it, but for many people with valid travel reasons, they need to make sure potential issues get smoothed over before they get to the US border.