Well I suppose I would trust a tax attorney to take the heat for me if he or she screwed up my taxes. But yeah the same security issues exist in those professions.
I have no idea what specific tools the pros use for their tax businesses. But at home I simply refuse to use any "cloud" service that doesn't at least claim to give me control over data-at-rest encryption in their cloud. That means no Google Drive (or hardly anything else Google sells or gives away), no Microsoft OneDrive, no browser-based password vaults, etc.
I use KeePass for account passwords, CrashPlan with a local encryption key for file backups, etc. It's all on me if I forget my complex passphrases for these apps. There's no second or third party that I trust to "escrow" those secrets with.
SSL/TLS transport encryption is based on a Certificate Authority architecture that's also got huge flaws -- why do web browsers around the world implicitly trust CAs from countries that most of us have never visited and in some cases wouldn't be allow to enter?
We can only fix so much but it starts with fixing what we can. That's why I push back so hard (mentally at least) against online tax preparation. Our whole U.S. income taxation system is way too complicated and really only benefits the professions you mentioned. We shouldn't be dragged into making our personal data even more vulnerable to theft and exploitation by a tax system that most of us abhor and only go along with at the point of a government gun.
