Common sense? I know it's not so common to begin with, but dude c'mon... Basic IT knowledge, lessons learned from your own and mistakes made by others, many years of experience?
AVs are useless
Wow! Not sure I have ever heard more naivety. Or is it total arrogance? Or both? It must be nice to truly be so much smarter than all the bad guys out there and therefore cannot be tricked. It must be nice to truly be so much more experienced, that one can easily spot every bit of maliciousness, and never, not once, even accidentally, let something slip by. It must be nice to truly be so sure every a piece of email sent from a trusted friend/contact or organization could never be infected - because, of course, they are so much smarter, more clever and more experienced than the bad guys too.
Wow.
"
AVs are useless"?

Right. So are vaccines, health insurance, air, food, and sleep.
and XP by default had an open firewall.
and your PC could get owned simply by being online.
What does XP have to do with anything today, or this thread?
I laughed at this.
Good times.. yarr be darr..
Actually, chrcoluk is right - kinda, sorta. When XP first came out, it had an integrated firewall, but it was disabled by default in part because many sites did not conform to industry standards and when the firewall was enabled, those sites were blocked by the firewall. And who got blamed by angry users? The sites for not conforming to industry standards? Nope. Microsoft got blamed.
So did users install the already established and respected ZoneAlarm Firewall? Some did (I did). But others just went on their merry way and got infested with viruses and worms by the bad guys. Did those users blame the bad guys? Nope. They blamed Microsoft.
So with XP "SP2", Microsoft enhanced the firewall and the UI and enabled it by default. But initially, it was for "incoming" data only - which "in theory" should be good enough. How could your computer send out malicious data if none got in. But the marketing weenies at ZA (later CheckPoint) and their fellow competitors and MS haters harped on the Windows Firewall incoming only capability, giving it a bad name - despite its effectiveness.
Example? One would think that Windows Defender would be very trustworthy and yet because of microsoft's many shady, skeevy, immoral and unethical activities, how can ANYONE trust it?

Come on Lex! Your clear and obvious bias and hatred for Microsoft has bubbled up to the surface again - and it is that bias and hatred that makes you not want to trust it, but worse, tell everyone else they can't trust it. That's sad. Holding grudges like that takes up too much energy.
Is Microsoft guilty of shady and unethical activities? Absolutely!!! No one, including me, could deny that. In fact YOU, Lex, KNOW I rag on their marketing weenies and misguided C-level execs for their questionable campaigns and policy decisions frequently.
But their
developer teams are different. They are professionals and care about putting out quality products. And they do AS LONG AS those marketing weenies and misguided C-level execs keep their grubby spiny fingers out of the code (and release dates).
So to your biased comments, (1) this thread is not about Defender so just another opportunistic, OT bash.

And (2), even the Microsoft marketing weenies and misguided C-level execs hate bad publicity! Especially when not due.
So FOR SURE - because of all the hate and bias against Microsoft out there like yours, "IF" Defender was the lousy, untrustworthy security solution you believe and try to convince

everyone else to believe it is, there would be 100s of millions of infected users out there, and 1000s and 1000s of bloggers and other's in the IT media constantly bashing MS for all those infected systems.
Where are they? They aren't there! Why? Because that is not happening. Why? Because Defender (or actually Windows Security) is a very capable security solution. Because TODAY, Microsoft can be trusted
when it comes to Defender - despite your clearly
unfounded and biased claims to the contrary.
And why? Because (1) the developers at Microsoft are professionals and care about the products they produce. And (2), because the marketing weenies and C-level execs don't want the constant, unfounded and biased bad publicity from biased MS haters like you.
Can we get back on topic again?