what if the most popular wallets also started implementing warnings and alerts that the inputs coming in their wallets are "possibly tainted"? How would that make the users feel and what would they do? Those coins would be sold right away, and if enough users are "warned/alerted" by their wallet app, it's probable that "tainted" Bitcoins would be valued less than "clean" Bitcoins.
It would be so weird and sense lacking. Think banknotes but you get less purchasing power the more used they look. Would mean we would have to play pretend every time. I could trade my 1 Bitcoin for some body elses 1.05 Bitcoin that were stolen from a kid. Then I would sell my 1.05 Bitcoin for 1.5 Bitcoin used in a hitman deal. Makes ZERO sense! But possible in todays world and not too far from where we are now.
I'm confused by your illustration, but to simplify, it's not really an issue today if we receive "tainted" Bitcoins because our wallet apps are not "warning" us or making us aware that they are "tainted". BUT that would would change if all wallet apps started using the services of blockchain analysis companies and make it easy for users to detect "taint".
With a community-wide awareness of "taint", exchanges, merchants and services would start rejecting transactions containing "tainted" inputs, making it harder for the user to spend or sell those coins, and therefore have lower value than "untainted" UTXOs.