I suspect you are coming from Windows.
But it’s antivirus software?
Since there are no known viruses for the Mac (just some malware), an anti-virus is unnecessary. That's why Malwarebytes for Mac is the only recommended software, since it is anti-malware. It takes care of the small number of threats for the Mac much better than Norton.
What’s wrong with it?
Norton has been known to cause many issues, from Kernel Panics to odd system behavior. Norton installs a large number of Kernel Extensions (kexts) which interacts directly with the macOS Kernel. The issue is these are very poorly written kexts, and since it is interacting with the Kernel, it causes Kernel Panics, which can lead to even more bigger issues.
Odd system behavior can include everything from unwanted bugs (from Norton) and just overall odd system behavior that makes your Mac not feel like a Mac.
How does it ruin MacOS?
In addition to what I said above, Norton has been known to set macOS System Files into Quarantine. Norton can't catch actual threats to the Mac, but it sure can set System Files into Quarantine.
I hope I am clear.
Cheers,
Jack