They do not know how to perfectly control it. Given the obviously huge scale at which they operate, it seems to work reasonably well. Yet the huge scale is exactly what scares the socks off of knowledgable people - even more than a fire here and there. Their PR problem is that the number of times they successfully work in the dark is somehow confidential...

You have got it right there! Breaking into a system is easy keeping yours intact is not. That is part that the US GOV still doesn't get the defensive part of the equation. BS (Before Snowden) people suspected but now we know people are listening everywhere. And even the NSA is not immune...that is scary that no matter how good your InfoSec is that your IA is lagging far behind.

It's the consequences, not their size.

"Look, we've put off 99.9% of the fires we started last week. Your complaint about we completely burning 2 cities down is baseless, you can't reasonably expect our fire-control to get any better."