>When you spend money, you basically say "I am one of 2^256 people", where 2^256 is usually fairly small.
Disappointing/embarrassing level of insight from a crypto project leader - here's a good layman-friendly video https://youtu.be/GEVm1dMn5Ks?t=14m to bring you up to speed (the simplified example is continued at 20m).
I mean, your argument "you're stupid, look at this youtube video" is not very convincing either.
Step 1: make a bunch of addresses Step 2: the world know it was you
That reduces the anonymity set for everyone else. They thought they were mixing with you anonymously but now that you are revealed, your participation in the mixing is useless, people would have done better to select someone else.
Combine this with Sybil attacks, criminal investigation, and other unmasking techniques and you might get the anonymity set down to 1 for a particular output, allowing you to further reduce other anonymity sets.
I was not aware, but apparently the Monero blockchain has a snowball effect to help mitigate this.
Basically, unless you own 80% of the outputs on the blockchain you don't have enough to identify subsequent transactions, so any foothold you gain in owning outputs becomes rapidly weaker. Given the cost of owning 80% of the blockchain outputs, it's not an attack that is particularly effective even at Monero's current state of usage.
Individuals who publish their input history won't make any significant difference.