While this is technically correct, it is the wrong response to GP.
Yes. ProPublica is biased to look in certain directions. Every single reporter, editor, publisher, is biased in this way. The answer to this is more, not less.
FIRE rose from decisions the ACLU took about representing cases. This is a fundamentally good thing, speaking as a diehard ACLU supporter.
Speaking as a huge fan of ProPublica, I'm hoping that they're investigating all of the supreme court justices (for example), because we won't pass laws to reign in judicial corruption without bipartisan action. But if they aren't, I desperately hope that there's a market for a conservative-focus investigative outfit that can stick to the facts like ProPublica.