Using your opponent's form of communication (power) undermines the argument in your cultural language (reason)

Kind of an epistemic and rhetorical issue raised in the tweet below.  From a Classical Liberal perspective, Kamala Harris's race is irrelevant as is the fact that her ancestors might have owned slaves.  As is the fact that her parents were immigrants.  We judge individuals and we judge them for their own actions, not the actions of predecessors.  

That she spent her career locking up people on weak evidentiary grounds, sought to suppress evidence of innocence, and sought to use her powers as Attorney General to go after political opponents are good reasons to be concerned about her candidacy.

Some permutation of that would normally be the Classical Argument.

In this instance, Barnes appears to be attempting to mimic the language and arguments of the DNC Left, focusing more on racial identity and collective guilt than on her personal actions.   

Potentially this sows the seeds of division within the DNC (I am not seeing her being a candidate that would appeal to Antifa, BLM, Social Justice or Bernie bros.)  Potentially Barnes's argument dissuades law-and-order conservatives from viewing her as having redeeming attributes.  Conservatives tend to favor law-and-order over abuse of power.  That she locked up marijuana users has no appeal to those concerned with rule of law and equality before the law.  Abuse of power by the state (and its agents) is something they are always on the lookout for.

So, in some senses, it is a good argument, using Saul Alinky's Rules for Radicals, particularly rule 4 ("Make the enemy live up to its own book of rules."), 6 ("A good tactic is one your people enjoy"), and 13 ("Pick the target, freeze it, personalize it, and polarize it. Cut off the support network and isolate the target from sympathy. Go after people and not institutions; people hurt faster than institutions")

Barnes is using the opponent's form of argumentation and thus might end up being effective. 

But it is unconvincing to a Classical Liberal because it is focused on seizing power from an opponent rather than making a persuasive argument that is empirically and logically coherent.  

In order to appeal to disaffected black voters who might lean toward protest voting (Kanye) or not voting (2016), Democrats ingeniously picked the one black candidate whose parents are not from America, whose ancestors had slaves, and who spent her career locking up black men.

— Robert Barnes (@Barnes_Law) August 11, 2020