If someone posts here saying "Help! My Bitcoin transaction won't confirm!" and I reply to them saying "PM me your 12 word recovery seed, I will speed the transaction up for you.", you should rightfully accuse me of being a scammer and warn him not to turn over his Bitcoin to me.
Correct.
If I replied that "You're completely ignoring the possibility that I'm trying to help!", you would explain to the user that there is no absolutely no need to trust me.
Correct.
That's exactly what I'm doing right now: I'm warning everyone that you are scamming because you are telling them to turn over control of their data and funds to a "Mixer" on a thread about coinjoins, which never give up control of a user's data or funds.
With the exception that using a mixer comes with some advantages over your service, and any other coinjoin service; cost and effectiveness. If there was an identical service available elsewhere where custody is not relinquished, then there would be no reason to opt for the custodial approach. But, in the case of coinjoin services which treat the currency as non-fungible, and fund the surveillance of the chain using coinjoin fees, I completely acknowledge the need for custodial such services.
Now this is the point where you reiterate the same misconceptions regarding effectiveness and how relinquishing your data negates the mixing purpose. Just to preempt this, I am specifically referring to services that don't keep logs. Moreover, I am fully aware of the risk associated with placing trust solely in someone's reputation.
If everyone coinjoined instead of using mixers, there would be no possibility of chain surveillance.
Except from the part where everyone can't coinjoin as there exist "naughty coins" which don't pass the zkSNACKs' approval? And the part where you're literally funding chain surveillance?