To protect them from accidentally speaking their mind, mentioning things that might get them in trouble if the other side hears it. to prevent this, Zoom (and others) ask you to click to open the mic. It's a GDPR thing: The default setting in most tools is that the user has to actively switch on their camera and microphone when they begin to participate.
Auto-muting new users is not the issue (every reasonable video chat software does this). The problem is that in Zoom you have to "join audio" before hearing anything. I guess they do this since you could in principle also join the call by phone. Anyway, this behavior is extremely confusing for inexperienced users.
Ah, thanks for clarifying, I completely agree.
> you have to "join audio" before hearing anything
If it's a private meeting, you're going to listen only, but
you're at a public place and didn't yet plug in your headphones?