To add on to this, even with the reticence many of us approach Mint with, it has the reputation of Intuit behind it. What can you say to alleviate these fears?
(directed at Penny)
(directed at Penny)
The other aspect is that banks are really good at physical security, but not so great at data security. Consider the recent Chase breaches, where a ton of sensitive data was leaked—you're obviously placing a lot of trust on Intuit or Plaid whenever you use Mint or Penny, but at least they're modern technology companies that probably hold themselves to higher data security standards than your bank.
Except this doesn't actually improve your banks' security at all, it's only adding another (attractive and high-value) attack surface in addition to any potential vulnerabilities that your financial providers may have.
Maybe the friction would be too much for most users, but I'd be way more likely to try something like this if there was an option to handle the data myself with an export/import process from my financial providers and not have any account credentials shared at all.