There is a way to encourage people to show up and vote for progressives in primaries, without excusing the DNCs undemocratic policies, dismissing the not insubstantial concerns of the left, and outright lying at the same time.
Example sentence: "Yes, the DNC did do Bernie dirty and manipulated the process, but we must not let us stop us from showing up to the primaries and making our preferences heard."
By doing the opposite of that it only serves to reinforce the idea that centrist neoliberals don't give a fuck about progressives, aren't willing to work with the left even if it means losing their support, and are willing to gaslight and straight up lie to push their agenda.
Characterizing people who are understandably upset at the biases, manipulation, and underhanded techniques of party leadership as them "throwing a hissy fit" is myopic, condescending, and ignorant.
Both sides are bad, and this is a prime example of why that is.
Again, that didn't stop us from practicing harm reduction and voting for the lesser of two evils in the general elections.
Even if that weren't the case, blaming leftists for the DNCs fuckups is only going to convince us that we will never get anywhere by trying to get the Democrats on board with progressivism and that a strong 3rd party is our only option if we ever want to have a hope of seeing effective leadership.
I don't think that strategy would work in the short term, and it would probably take the Dems and Progressives losing at least one more election to the fascists before we could gain enough support to win.
I'd rather the Democrats stop being a barrier to progress, but it looks as if they aren't going to give us a choice and people like you excusing their behavior is only going to help make that a certainty.