Despising Sinner's fanbase in case they deliberately support a doper makes sense.
However, I don't think anyone supporting Sinner after the revelations believes him guilty of intentional doping. It seems you think otherwise and thus you may consider their opinion to be misguided. But despising anyone with a misguided opinion seems like an overreaction. Most likely, all of us have a fair number of misguided opinions. Personally, I don't believe Sinner to be guilty of intentional doping, but I don't despise people just because they disagree.