When I was in elementary school, there was a wordplay prank kids pulled on each other by asking "What are you eating under there?" When their target, confused, responded with "Under where?" they'd laugh and shout "You're eating underwear!"
No one was actually eating underwear; no matter how upsetting the mocking was, it did not change the truth. Similarly, responding "What?" to someone quickly whispering "Idiotsayswhat" does not make you an idiot, or any of the other wordplay pranks.
J.K. Rowling can say "Engaging at all with Harry Potter fandom means you support my political ideology!" all she wants, but that does not make it true. Especially when you consider how many people blissfully go through their lives ignorant of social media. The Drarry shippers and 8th Year gen ficcers and the grandmother in your knitting group making a Hufflepuff scarf are not inherently supporting Rowling's crap just by doing those things.
Directly giving her money potentially allows her to donate more to her favored political causes, sure. That's also true of any other author, editor, artist, actor getting residuals, movie producer, musician...Hell, it's true of tipping your barista and buying carrots at the farmers market.
I'm not going to give Rowling any more money. I'm also not going to terrify myself by assuming the fellow shopper at the grocery store tossing the HP Keebler cookies in their cart wants me dead, or feed my scrupulosity by looking up the authors of every single book I check out from the library.
No one is eating underwear.