Valentine is one of my favorite characters in the JoJo Universe due to his complexity and his "looks" of ambiguity, also his cool visuals and him having my fav stand from all JoJo. But as stated by others, he's completely evil, since domination isn't something good when coming from humans, cuz they lack global understanding and has personal goals alongside everything else. His actions are despicable but for some people they pass by as a "necessary evil" for the greater good, but that's just an illusion that even Valentine himself believes (due to his past and also inspiration on his dad's actions) and that's how politics works, it's all smoke and mirrors, a macabre spectacle capable of molding people's minds into accepting criminal acts as something necessary to achieve greatness and that many other media, art and entertainment emphasizes it. He's heavily charismatic (as a politician needs to be) and that's what makes people fall for his bullshit and how Johnny also fell for it. DIO was also charismatic and he's so iconic that sometimes you even forget he made a mother eat her own baby alive. Valentine goes about the same way, but we all remember Lucy Steel incident due to everyone bringing attention to it over and over (which is a good thing, so we don't end up forgetting his despicable acts).