"defining" doesn't lead to bias. you are left-leaning regardless of what you decide to call yourself. The important thing is recognizing and acknowledging your predisposition, which it seems you have.
People are prone to bias regardless of their political identification. Identifying as left-leaning provides no more protection against bias than any other political identification.
I have had so many conversations from casual progressive conspiracy theorists about how they think all the Democrats get together and agree on the fall guy (most recently, Manchin) to keep issues on the table indefinitely. You see it constantly with these Jill Stein people. I've literally told them the only solution is to give liberal Democrats the majority, which they haven't had in my lifetime.
Those ones are constantly spreading idiotic takes. "The Dems and Repubs have a ratchet effect towards evil. Therefore we should let the Repubs in to advance the ratchet."
The things they cite as Dems holding the country back are like always direct results of Repub SCOTUSes, too.
Sure, drag agrees with the left on every issue and completely supports their policies. But drag thinks politics are like sports teams, and drag won't back a loser!