Each state has its own laws regarding elections and recounts, but in all the states I've looked at, voters have to sign either a document at their precinct if they're voting in person, or on an envelope for their ballot if they're voting by mail. If there are more votes in a precinct than there are in that precinct's voter registration database, or if they have a mismatch of signed envelopes or sheets and ballots, or the hash on the envelope doesn't correspond to the ballot, or votes from people not registered to that precinct, or multiple signed sheets/envelopes for a single registered voter, all of this makes the "they just dumped in more ballots in" theory more unbelievable, as the amount of coordination and access needed to successfully execute that theoretical tampering without leaving plenty of evidence becomes realistically impossible.

It's fine to investigate a hypothesis if you're willing to accept the hypothesis is false. But if you continue asserting your hypothesis is true after many competent investigators, including investigators ideologically aligned with yourself and your desired outcome, investigate the system and find no evidence to support said hypothesis, instead finding evidence that repudiates your hypothesis, well, it's bad for democracy to continue pushing that hypothesis.