Couldn't you just use poloniex to get monero bought with BTC, then send it to yourself with a mixin of 5 or 100 or whatever you choose, then convert it with XMR.to back to BTC?
That's centralized and you lose control of your coins even if temporarily. Coin Join allows for mixing without ever giving out your coins or control of them.
Any exchange or gambling site or online wallet will do what you suggest. You just have to trust them to be online long enough for you to withdraw, and/or not get hacked, shutdown, or whatever.
I've actually seen a few people deposit to my site, wait a few days (when I "join" all deposits to the cold wallet), then withdraw, without ever playing. Works the same way. But now their coins are "tainted", so don't go try going to coinbase directly from any gambling site. Our wallets are all tagged.
I'm speaking in terms of privacy. What's to stop someone from being all the "other people" in coin join transaction?
Essentially being Sybil attacked in terms of traceability.
The topic was privacy Not security.
The issue you bring up comes back to, how did you acquire the bitcoins you want to "wash" in the first place if you didn't mine them?
Pretty sure there was a "not being in control" aspect to the acquisition of the Bitcoin you are trying to use in a coin join Transaction. Kind of goes against what you just said in terms of centralization and security of your coins.
Concerning your comment about your bitcoins being tagged.
That cannot easily be done in monero due to its protocol based fungibility via ring signatures.
