Yes, it's a bad idea. Bugs me frequently. But...it's so dangblasted useful; throw some social/emotional motivations in there and a bunch of problems get solved well enough to tolerate the risk. Given Intuit bought Mint, and I've trusted my taxes to Intuit for decades, I'll grudgingly take that risk to solve other problems.

A core issue is the need for a next-level financial data aggregator, somebody to pull together one's info across multiple banks, cards, investments, etc. Much as Bank X wants to provide all those services to me, and much as I may even want them to, other companies get involved and there's a need for a one-screen view of all of it, preferably updated near-live, and working on whatever interface/device I choose to use (notebook, phone, tablet; app, web browser).

Trust is the main thing. I was mad at myself for signing up for Mint (in a fit of frustration attempting to solve some problem) when it was new & independent; I'm still irritated but less so now that Intuit is taking responsibility.