That's a very one dimensional view of evil. Characters are more than their alignment. Evil characters are people too, with their own motivations and interests. It's simply that one of their driving motivations is self-interest.
While an evil character could kill children and innocents if they wanted to (for example, their self confidence is low and doing so makes them feel powerful and in control) they won't do so necessarily. For example, a chaotic evil character might have had it rough growing up as a child and feel sympathy towards children. While he wouldn't hesitate to slit another man's throat for a corroded copper piece, he won't do so if there are children watching, and he's even likely to risk his own life to protect a child from harm.
Similarly, ambition and alignment do not correlate. A lawful evil character doesn't necessarily want to take over the world. Perhaps he has the much more reasonable of ruling the local thieves' guild.
In the recent evil campaign I played in, the party's overarching goal was to save our area of the Underdark from being enslaved by an "alliance" between the Illithid and the Aboleth. Which is certainly a goal that a good party would strive for (and indeed, when the Deck of Many Things turned half the party good, our goals didn't change; only our motivations did). I'll grant you that our party did some unsavory things (the worst of which may have been wiping out a colony of flumphs who were in the way of a duergar mining operation) but because the majority of the party was evil the ends justified the means. We certainly didn't harm any children, and for the most part we were going against other bad guys, not innocents. My character always treated those weaker than himself with respect and dignity, and even did what he could to help them out. Of course, he did this because he figured that they would be grateful to him and he might be able to leverage that gratitude in the future to his favor, but that's simply what was going on in the character's head. As far as any of the other players were concerned, my character was just a genuinely nice guy.
I'm not saying you should give an evil campaign a shot if it isn't your cup of tea. This game is meant to be fun, so if an evil campaign isn't your idea of fun then don't play one. It's simply that an evil campaign can have so much more depth beyond playing murderhobos who want to take over the world.