To keep bitcoins fungible and valuable everyone with a stake in bitcoin should accept and redistribute tainted coins as much as possible, e.g. using CoinJoin. When everything is tainted, nothing is.

Whether they have a warrant or not, these days they will invariably be a SWAT team who will break down your door instead of knocking. Either you end up with your face on the floor and some asshole's knee in your back as they ransack your house, or you get machine gunned because one of them thought you might have had a gun. Either way, if you have a dog, it gets shot.

Exactly

If you even have to do this in some jurisdictions, then Bitcoin has lost its fungibility, which is harmful to the value of all bitcoins in all countries.

How would you feel not if but when this happens to you?

You saved up about 1,000 BTC.  One day, a group of local police shows up on your door.  Mr Richy, we looked into  your BTC Transaction history and learned that you have 0.00001 BTC from the Pizza heist.  We are here to serve the search warrant to take all of your computers, smartphones, tablets and external drives and even the PS4 game unit.  Oh, by the way, we seized your BTC Wallet Address for further investigation.  We will let you know when you can claim your stuff back.  

(not to be mean, but please expect about a year or two of the wait.  By the way, we will send you a Tax Due Letter on your Total Bitcoin Value.  You can come up with all the transaction logs and may be able to claim some tax deduction, but you need to hire an accountant to do that.  Have a nice day!  Oh....  Sorry, that Toyota parked in front of your house, we are impounding that car because it appeares that you paid a portion of that car with the BTC Wallet that had a tainted BTC fro the Pizza Heist, so when you prove you didn't do the heist, you can come to the police station to get your car back, ut until then, your car is held by the POLICE.)

Oh, one more thing, we only accept cash for the impound fee from you because we seized your local bank account and the stock trading account and the retirement accounts because your wallet had the tainted BTC and therefore, we suspect you committed the financial crimes.  )

A week later, you'll get a few phone calls from the criminal defense lawers trying to sell you their service but ask for Cash or some discount via BTC.  You retain them with $25,000 USD.  3 months later you get everything released to you except the computers, tablets, cellphones and the hard drives.  By then attended a few court hearings and legal bill exceeded $80,000 USD.

After $150,000 USD later, you were offered a petty offense/crime deal for possessing the portion of the stolen coin.  2 years of probation/supervisory release.  Have to attend meetings, piss in the cups, blow in the tube every few days, work in the chain-gang for a few weeks.

A few years later, at your son's wedding reception, he apologize you for borrowing his BTC account to view some porn and he returned 0.1 BTC he used to pay for the porn site, he made enough BTC via ads clicking/BTC Faucent and paid him back with some interest.  Dad, than you for not giving me up to the police for borrowing your BTC for a few months.

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Or a mom with 3 little kids at a local Walmart buying some milk and cheese.  She sees and hear another young mother trying to buy food in the next cash register was short of $20.  Nice lady helps this poor mom, in return she was offered 0.1 BTC just for helping her out at the cash register.  Exchange the coins at the register via smartphones.

3 months later, big bangs go off in and outside of your home at 5:45AM in the quiet middle class neighborhood.  You could her dogs barking and loud voice saying Federal Agents/Police.  Someone is running into your bedroom while you are butt naked, ordering you to drop on the floor and hands above your head.  Male Officers pat you down and handcuffs you naked while your kids crying.  After everyone looked at you naked, you could hear them screaming where is the computers? (You don't own any computers & anything close to it would be just 1 Samsung Galaxy.)

You were receiving the child support or out-of-court agreed monthly child support via BTC from the father of 3 children.  Police takes your cellphones.  Seize your BTC Wallet Address, and you get charged associated with a 4.1 Millions Doller theft from one of the Chinese Exchange Market.  Police said 2 BTC you received last month from your EX was traced back to the Exchange Heist in Hong Kong and you were investigated for possessing and using the stolen BTC (RED LISTED BTC.)

May not happen this way, but just a thought...

Really scary what seems to be popping up lately ... with the "Coin Validation" crap and now this.  Makes me really glad I didn't join the foundation.  Really looking forward to Dark Wallet and mature CoinJoin implementations!

Besides all that, I really believe such systems wouldn't work; what if I had a "white-listed" address tied to my identity and bought some discouraged things or services with it?  "Oops, someone must have stolen my private key.  Didn't look at my saving wallet for some time, so thanks for pointing it out to me.  Really sorry for all the rest of my nice coins in there!  Damn hard to secure your system it seems."

That's not very good either since it breaks Bitcoin in a different way.

Satisfying the conditions of the appropriate script must always be both necessary and sufficient to spend an output.

I agree we can't prevent governments corporations from doing this. However putting support of this into bitcoin-qt would greatly accellerate acceptance of the scheme. Fear would make it work.

The answer to ransomware is tightening security and switching to opensource software, not fucking with Bitoin.