Well I subscribe to moral relativism, so I don't have an issue with you not finding it to be unethical. But personally, it bothered me that so much user data would be mined from their financial statements.
I know B2C companies like Mint do this as well, and I don't have an issue with user data being used for market research. But it seemed underhanded since most customers aren't aware of it. If you use Mint you can read their T&C and understand your data is mined. But Plaid is not sold to users, it's sold to companies. So end users of a completely different company which simply uses Plaid for account verification would be implicitly volunteering their data.
The other thing that bothered me is that companies which have valid reasons for not wanting to develop API integrations for Plaid would be strong armed into doing so once Plaid had acquired a critical mass of their users using the methods I helped them develop.
