Why are people upset that a misunderstood "Villain" is being seen as a Villain by other people....
who don't understand what he has been through? People have to remember that characters in a story don't have the 3rd person view we do. They don't know about Stanwick's betrayal, like we do, and as such they have to fill in the dots using Rumors, media, or newspapers, however false it might be.
Say that someone who had never heard of Viktor was watching the news, and the media described some crazy robot cultist leader named Viktor. That news from media skipped over "small" details about it being your choice to convert, he wasn't going to force you, or how it might benefit you. Why? Because it's the news, they want a headline story quick and easy to grab viewers attentions, how ever false or uninformed it might be. So people become uninformed and from their views that Viktor is evil.
Not everyone knows how Viktor was betrayed, and certainly a lot of people aren't going to understand why people would want to become a cyborg/machine/whatever, and as such people are going to view Viktor as a villain, a danger to their normal, every day life. For all we know, Jayce is further hurting Viktor by spreading propaganda to further spread his name about Piltover.
TL;DR: People do not know Viktor's backstory. He is viewed evil by those who are uninformed or scared. Just because they are uninformed, does not mean they are right.
p.s jayce sucks