The Left understands the power of symbolism to change people's thought patterns. They're using this particular symbol as to reinforce their "Dead White Males = EVIL, 'Minorities' = RIGHTEOUS" meme. Who appears on the $20 may in itself be trivial, but the agenda behind it is not.
It's the same issue that I had with the push by liberals (and establishment Republicans) to remove Confederate Flags and memorials. Even if you have no particular sympathy for Neo-Confedrates, the symbolism of the act is about the PC Left's power over how Americans choose to remember their heritage and history.
The people who pushed replacing Jackson with Tubman also want to replace Washington with Malcolm X. Those who want to tear down the Confederate Flag also want to burn the American flag. They just aren't there yet, there would be more resistance to defiling Washington's memory than Jackson's or Robert E. Lee's. They go after the easier targets first, and count on reactions like yours to make sure the PC Left ratchets forward, slowly but surely.
DWEMs are still all over the rest of the money we have.
I am okay with the symbolism that allows someone other than DWEMs to be honored here and there.
It was Congress who put them all over our money, and I’m okay with our more or less democratically-elected Congress tweaking it here or there.