False, unless you like to live dangerously.
It used to be the case that bad guys didn't target Macs. It is still true that it's harder to infect a Mac with malware than it is to infect a Windows computer. But Macs are vulnerable to malware, and the risk is only increasing. You should have a good antivirus installed and running at all times. Here's a list of the best free antiviruses for Macs in 2018, courtesy of Techradar.com.
You'll notice that AdBlock is not on that list. That's because AdBlock is not an antivirus. It's an ad blocker. You say you don't mind that downloading a page full of ads takes twice as long as without the ads? Fine; maybe you use that time to learn Tuyucato or master boeuf bourguignon (or just learn how to pronounce it). An ad blocker, while not an antivirus itself, is still your first line of defense against compromised ad networks that can spread malware.
And let's not overlook the threat to your privacy that ads represent. Everywhere you go online, advertisers are tracking the websites you visit, the pages you open, the search terms you enter, the items you place in your shopping cart and don't buy, even the forms you start to fill in but don't submit. An entire industry has grown up around creating eerily detailed profiles of you that are then sold to third parties, which use your data to target you with even more ads.
It's fine to allow ads on sites you choose to support this way. But not having an ad blocker at all puts the advertisers, not you, in control of your browsing experience—and your personal information. Which do you trust more to keep your data, and your computer, safe?