STP failures and flaps can cause outages, but requiring an admin to manually move patch cables and activate hardware almost always causes larger, longer outages.
Yes. But how often have you had an untouched cable fail? Maybe once in a lifetime career? How many times should you expect STP to take down a network? I've seen that happen many more times. Though, touched cables fail often. The barely-on connector that fails when you brush it getting to a power connection on an unrelated piece of gear. But, you are right there and prepared for it, so you can fix it before STP convergence time.
(And I'm not involved in networking in our team, I look after servers and applications).
Good, because 802.1x isn't MAC authentication, so MAC spoofing is unrelated to that topic. And your solution of active/active load balancers still leaves you with a single point of failure. Active/active, by definition, has a single configuration across the devices. So one typo on one device can take down both. Back to a single point of failure.
A routing protocol, by its nature, can't be a single point of failure
Yet, and improperly injected route can take down the entire network. Single Point of Failure.
That does not make me filled with hate
Sure it does. You hate Hillary. You are voting for a moron, so you said.
And no, redundancy doesn't make things harder as long as it's implemented properly
"properly" by your definition is prohibitively expensive. Almost nobody does it. Realistic redundancy leaves lots of gaps and holes. And in many cases, active/standby is dangerous. HSRP, STP, and many other protocols are active/standby with errors in the standby allowing massive networking failures. And, of course, the protocol to manage that redundancy is a single point of failure. You could abandon HSRP to avoid that single point of failure, and instead have multiple gateways and every endpoint running a dynamic routing protocol but that just moves the single point of failure to whatever routing protocol you pick, and isn't generally done for a variety of very good reasons.
Nope, the simplest network is often more reliable than the rube goldberg redundant networks I've seen experts like yourself put together. KISS is one of the first rules, and the more you know, the more it matters. KISS. Anything else is expense for the sake of complexity.
Parkinson's Law: Work expands to fill the time alloted it.