Why does the history matter? We all receive cash that has been used to buy or sell cocaine, we know it. So what? For once more, coin history a privacy problem, not a fungibility.
Let’s say you want to buy some bitcoins but you can’t buy it from an exchange for some reason and I happen to own some coins on sale. So are you telling me, it wouldn’t make any difference to you if I wanted to sell you some coins with very bad history? (Maybe Isis used my coins to fund their operations or I got my coins from an exchange hack and I am that hacker) I want to sell you my coins directly, without using any third party exchange/mixer. Would you take this deal? (You want to buy coins and I am the only option you have, this is the situation basically)
According to your logic, you should.
If you say “no”, now you see why it matters.
It is exactly the reason why some bad people use mixers too. It is because they can't spend these coins. Nobody wants them.
Regarding your question, I think some people would accept them,
but they would probably ask for a discount (maybe up to 50%). Paying 0.5 BTC for 1 "tainted" BTC would seem like a good deal. As always, it's the free market that dictates what should be done.
Some would even exchange it for XMR afterwards, temporarily at least.