I'd argue it's way more possible for a private company to have the public's interest at heart than a public company. Obviously a company needs to make money to survive, but the necessity to make enough profit to survive as a company doesn't preclude any kind of public interest; the two aren't mutually exclusive.

Unfortunately, they do often overlap a lot less than they should, often just so the company can make even more money. It could be argued that there's some bigger picture ploy in the form of "if we make more money, we could help more", but obviously this gets into a case-by-case basis analyzing companies -- some fit the mold of having the public's interest at heart, and some don't, but all of them are on a spectrum both for public interest _and_ how well they implement it.

This is completely disregarding the fact that what is "right" for "public interest" varies from person to person. One person of the public might very much want total surveillance and one might not want anything to do with technology at all -- is building something for either really in the public interest? The common sense answer is no: "public interest" defines what the _majority_ of people want (which has its own issues), but even that changes over time.