Let's start with Netserk's picture from the OP. Fool me once... you know how it goes.
I believe doping is a necessity to become really succesful in this sport (probably in many sports), and I can fully understand why some riders decide to go all in on realising their dreams and potential (either on their own initiatives or due to pressure from people around them). To paraphrase Michael Rasmussen: If you've already decided to break the rules, you're only cheating yourself by not going the extra mile. And as I said during a presentation at school 16-ish years ago, I have no reason to believe I couldn't get persuaded, if I had been a pro rider.
However for me as a fan, there's still a line that can be crossed, which happens whenever a rider and/or team are no longer just doing the bare minimum or slightly more and moves into the top bracket of doping users (I am a hypocrite though, cause it doesn't always mean I completely stop supporting riders or teams. Otherwise I wouldn't have continued to be a Samu or Martin Fourcade fan after they started to do ridiculous things, for instance).
Denmark has now had tree riders who have had the esteemed honour of being able to win the biggest race and thus being crowned the king of the cycling world. One of them was a bit unlucky to be denied the chance to actually win the Tour, while another was fortunate enough to stay around for years before admitting guilt, although there had been evidence circulating for some time at that point.
Now we have a third guy at the very top level of GC riders. Vingegaard got his breakthrough at an earlier age than the other two and is in some ways both more believable and less believable than them. In Riis' case he rode for Gewiss Ballan and Telekom who were among the most ridiculous teams at the time. This wasn't always the case for Rasmussen at Rabobank, but it's definitely what's happening with Vingegaard and Visma nowadays. I therefore can't root for them. I can't deny that I've held some grudge against the team ever since the Rasmussen debacle, but it hasn't always kept me from liking their riders.
Another reason for my dislike has nothing to do with Vingegaard himself, but the Danish media and other Danish fans' reaction to him. It's of course very understandable that the media builds up a hype for an athlete, but I wish they would tone it down a notch and be more critical of him and his team. We know they will throw themselves at him if/when he ever falls from grace, but that fall could be way smaller if they did their job differently.