You need security beyond what’s built into macOS.
Ransomware and other types of attacks on Macs have made the news. But don’t think that means your Mac is immune. You’re a lot more likely to encounter a malware attack on the Windows box, both because Windows (despite Microsoft’s ongoing efforts) is still a more vulnerable operating system and because malware coders naturally target the platform with more users. Put a Mac and a PC on your desk, hook both up to the internet, and start surfing all over the web with no antivirus protection.