In that case they are being idiotic. It only takes one person doing something on a compromised internet connection (Captive portals that replace certificates,

In that case they are being idiotic. It only takes one person doing something on a compromised internet connection (Captive portals that replace certificates, etc, etc) for your "confidential" information to be leaked. (Note: if said cloud storage does encryption on top of HTTPS and/or proper certificate pinning (although this can cause other issues), this may not be the case. But that is not true too often, for example with web interfaces.)