[krapp]

You can't. Independent opinion doesn't exist - you would have to validate every datum you're presented with starting from first principles, which is impossible.

Accept that most of your opinions will be informed by the opinions of others, likely directly, and your method for judging truth will instinctively be biased more towards emotion, social status and ego-preservation than than logic and fact, because humans are social animals and that's just how we're wired.