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Chris Messina, credited with inventing the hashtag, may not be a household name, but he's well respected in Silicon Valley for his work on communities, social networking, and identity. That's part of the reason he was recruited to work at on a super-secret new project that came to be known as Google+.

Messina spent more than three years working as a designer on the service until August 2013 when he left Google to pursue other projects.

Of course, there's been plenty of debate about whether Google+ has been a success, a failure, or just something that's hanging in a puzzling limbo at Google. Earlier this year, the executive who oversaw Google+, Vic Gundotra, left Google, adding to speculation about how committed the company is to the service's future.

But in a new post on Medium, Messina makes it clear that he's hugely disappointed in the way Google+ has turned out. He believes the company missed a gigantic opportunity to re-invent social networking in a positive way for the future.

'Lately, I just feel like Google+ is confused and adrift at sea,' he wrote. 'It's so far behind, how can it possibly catch up?'

Why does it matter? Messina argues that it's essential for everyone that Facebook has a robust competitor and that users feel like they have a real choice in terms of who controls their social networking activities and identity.

'The future of digital identity should not be determined by one company (namely, Facebook),' he says. 'I still believe that competition in this space is better for consumers, for startups, and for the industry. And Google still remains one of the few companies (besides Apple, perhaps) that stands a chance to take on Facebook in this arena - but Google+, as I see it, has lost its way.'

His criticism is that Google failed to seize the opportunity to rethink our notions of privacy and identity on the Web. Messina believes that there is room for a service that helps us make better use of our personal data in a positive way, that encourages us to share more because we trust it, and as a result, improves our online experiences dramatically.

Instead, he argues, Google took an uncharacteristically conservative approach to building Google+, worrying more that it would fail and simply trying to mimic Facebook, rather than trying to build something revolutionary.

'Why did the world need another Facebook, unless to benefit Google by making their ad targeting more effective?' he writes. 'Why wasn't Google+ one of Google's famous moonshots, intended to improve personal social networking by 10x? Why did they take a conventional approach to social networking rather than think about what controls people might need in the next 5-10 years in their digital lives?'

Messina, in the end, wants to be hopeful about the future of Google+. But he has hard time seeing how things change.

'The fundamental problem that I have with Google+ is that I just don't understand it,' he writes. 'And what I don't understand makes me nervous  -  and should make you nervous too.'

This article originally appeared at VentureBeat. Copyright 2014. Follow VentureBeat on Twitter.