First of all, the reason it should be taken out of the hands of politicians has nothing to do with whether either/both sides engage in gerrymandering. A simple case about conflicts of interest is sufficient without ever having to point fingers at individual parties or individual politicians.

Second, it DOES matter that when you accuse both major parties of doing something unethical that you don't do so in a way that suggests (implicitly or explicitly) that all parties do so equally. Things like voter apathy, low voter turnout, voter disenfranchisement and much of the existence of voting for inexperienced "outsiders" with no ability to work on politics happens when people feel like all politicians are the same, all political parties are the same, etc. If the entire country genuinely believed that, despite their faults, the Democrats were on average more interested in looking out for their best interests and operating ethically then more people would vote for them. With intentional and unintentional narratives of both parties being "the same" and "equally bad", partisanship will just get worse.