In my opinion, Patreon is more akin to a newspaper deciding which ads to show next to their articles or to a shopping mall deciding which shops to rent space to. And of course every newspaper will reject ads that would infuriate their readers (or journalists) and shopping malls will not rent to businesses that might damage their reputation (depending on how "upscale" it is this might be everything from soup kitchens over gambling outfits and payday lenders to brothels).
Now, you might disagree with them whether they have drawn the right line there and consequently take your business elsewhere (just as you might not want to visit a shopping mall with the wrong mix of shops), but I find it a bit of a stretch to frame this as a "free speech" issue.