WHOIS was useful...
Well it would have been if it had been done properly.
It was useful to be able to check that an owner was legitimate - but even more useful if the WHOIS data was properly validated so scammers couldn't buy a domain and give fake details.
It was useful if there was a domain you might be willing to sell or one you might want to buy, easier for the two parties to get in contact.
If there was an opt-in/out option the domain owner could decide whether they wanted to be listed and possibly what level of detail. Domain name owners could make their own choices and anyone making a whois search could make useful inferences from those choices.
I used to run an internet business, we would register domain names using the customer's name as "owner" but with our contact details. That meant we got all the spam and, as it usually had fairly predictable content and structure, it was easy to filter the garbage and respond or forward any legitimate messages. Our concern was that end-users were not good at spotting the scams and might respond. Before we started using our contact details the most common queries we got from our customers related to fake domain name renewal emails and the "someone wants to buy [your domain name].cn or .asia, if that's not OK we will secure it for you" scam. We were concerned that some might not check with us first and pay-up.