Here’s a great post on the two main kinds of sportsbooks, “sharp” ones that allow skilled bettors to play and actively shift their lines, and “soft” ones that focus more on marketing/entertainment, just follow the lead of the sharp books regarding lines, and will, often massively, stop skilled bettors.
As for the ethics question of it, well, I do think soft books are unethical the way that other types of gambling are unethical. After all, I remember very well all of those New York State Lottery commercials promising riches just one ticket away. And the highest margin business model of sports betting is often called the “parlay lottery” for good reason.
Though to be fair, the odds have to be staked in favor of the house for the sportsbooks to survive at all. The analogy I use is basketball. If it’s a soft book, you’re playing a rigged carnival version. If it’s a sharp book, you’re playing one on one against a pro player who’s good at stealing the ball even from other pros. As betting expert Joseph Buchdal put it:
“How about this one [warning label]: “95% of sports bettors will lose at UK bookmakers. The other 5% will be banned. 99.9% of sports bettors will lose at bookmakers who let you win.“