That's not necessarily true. SSL/TLS does not prevent all MITM, it prevents unwanted MITM.
To be fair, I don't think you can install certificates on a Chromecast for example, so it might not be practically feasible for all devices, but a blanket "SSL makes that impossible" is not correct.
You can always choose to install your own root certificates, at which point your browsers will trust any certificates issued by them (which could be your own mitm proxy)