The point isn't that they never publish an opinion piece, it's that they do publish investigative reporting, like this:

https://www.cato.org/blog/why-nsa-deleting-call-records

You also get pieces like this, which are full of factual information whether or not you agree with their policy position:

https://www.cato.org/publications/policy-analysis/new-nation...

And it's hard to see which "corporatist agenda" pieces like this are pushing:

https://reason.com/2019/11/21/with-this-forfeiture-trick-inn...

Which isn't to say that they're unbiased. Everybody has an opinion. But everybody has an opinion; that's why you need more than one news source.

There's massive amounts of special interest money being funneled into publications on every side of issues, local and national. That's the reality we have to live with. See Politico's latest reveal of "dark money" also going toward left-wing policy activism and media coverage [1].

That doesn't mean we should totally ignore what media and think tanks have to say, they can still produce good critiques and investigations -- whether Brookings or Cato. Even explicitly partisan muckrakers like Greenpeace or O'Keefe's Project Veritas occasionally expose a valid case of wrongdoing no one else noticed. These organizations are very selective and hyperbolic in what they focus on, due to their narrow mission and ideology and the natural limit of time/energy, but if you combine all of their varied output you can get enough slices to approximate the pie.

[1] https://www.politico.com/news/2019/11/19/dark-money-democrat...