There may have been a stigma to some and not to others. I know that when the idea of blood doping came out and that it was not against the rules some of us were intrigued and wondered how we'd go about doing it. As far as I know, no one that I knew ever did but I think many of us thought of it as similar to the depletion diet that we did before marathons.
I get why some people think it was cheating even if the rules didn't forbid it but here's the difference. If a recent Olympic medalist is found at a later time to have been using an illegal PED, or having blood doped in recent years, while winning his medal the medal is taken away from that athlete. If there was ever irrefutable evidence that Viren had in fact blood doped nothing happens. He keeps all the medals because it was not against the rules and therefore not officially considered cheating. I think the situation is similar to the one involving altitude tents now. Plenty of people object to their use and attach a stigma to using them despite their legality.