Sports betting is the ultimate second-person game; no individual bettor is the one throwing the football. But somehow, I guess on the back of lobbyists, that's more acceptable than first-person games of skill. It's ridiculous.
I would consider it somewhere in the middle-ground between poker and roulette. It's possible to have an edge in sports betting, it's just very, very hard to find.
The databases these poker players kept led them to discover the scandal mentioned below, see: https://upswingpoker.com/ultimate-bet-absolute-poker-scandal.
No such scandals were ever found at other big poker sites, despite that there were more, stronger players at those sites, which also allowed improved scrutiny of their random number generator and the play of everyone involved.
In practice losing/casual players tend to lose their money pretty quickly, and winning/skilled players then take that money that they've earned and withdraw it - while waiting for another casual player. The house has every motivation to increase the amount of time it takes for a skilled player to wipe out a casual player. They also benefit from casual players going on 'hot streaks' early on. The goal there is to convince the casual player that they are skilled, and their later losses are "bad luck." The point being to encourage them to deposit more after they lose their money.
In an online game, how do you know other people at the table aren't side channel communicating? How do you know some of the hands aren't player bots that work for the site where whatever money you lose and they win goes to the casino site? How do you know they don't know the precise order of the "random deck"? Or that they don't know what your hand is?
Now, consider the same for voting machines.
It does make sense that in a lot of player-versus-player games, online makes it more risky.