They are two different issues, really. You'd be just as arrested for committing crimes on a neutral or un-nutral net, a nutral internet doesn't mean an archaic one. You commit fraud online, you have committed fraud just as much as if you'd done it in person. You commit identity theft online, you have committed identity theft just as much as if you'd done it in person etc etc etc. Harassment, hate-crime, stalking etc - there are consequences to actions, even online.
The question is would you find yourself in the cells if you got on a soap-box on the corner of the street and started yelling the things assholes put in comments sections and forums online at members of the general public passing you in person?
If I said "you have dubious personal hygiene", that's a mean thing to say - but if I said it to you in person I would not be arrested for it. The things people get arrested for are usually more serious and the arrests are backed up with actual criminal laws...
I'm sure I don't have to repeat them, but you know the type of comments I mean - this link sort of covers it:
https://www.gov.uk/report-hate-crime and there are some legit criminal laws such as "Incitement of religious hatred", "Incitement of racial hatred", "Harassment" etc, which are also things that if you did them on the street you'd be arrested too... Legit crimes that they would be arrested for if they were doing it in person are often what people get arrested for putting online...
Even if not illegal there is just common decency and inadvertent harassment - there was the case of the guy on twitter who was arrested for posting "I'll bomb this airport if my flight gets cancelled" or something close to that. Yeah, it's obviously jokey - but if he was stood in the departure lounge yelling that, what would airport security do? Laugh along? nope, they'd take him aside and he'd
definitely miss his flight because they'd be searched his body cavities for suspicious substances.
Within 10 minutes of yelling some of the stuff people put online on the corner of a street, you'd be reported. within 20 minutes officers would be observing and within 30 minutes you'd be having your collar felt. The internet is just as public a place as the high-street.
There are also parts of the web that are not easily accessible to the general public via search engines etc. How many web-related arrests take place because of what goes on in the 'dark' web? Figures we don't have access to.