With gambling, the motive is unclear. But I would imagine it’s much easier to lose on purpose than win on purpose, making "lose on purpose" the more likely outcome-baseball is already a game with a lot of failure, and having 1/9 of your chances to actually succeed give up can be devastating to your chances. That’s not to say that players would only bet on themselves to lose, but it’s an option. If one side were trying to lose, it would be a scripted event, not a sport, and therefore, not baseball.
With steroids, there’s a very clear motive: play better. That doesn’t challenge the integrity of the event occurring nearly as much; it’s still a competition, at least.
And really, how is that motive any different than those for scuffing a ball, or corking a bat, or taking amphetamines, or any other number of things players have done? And yet, no one is calling for a lifetime ban for any of those. Why? You can say it’s due to how successful it is, as that doesn’t change the intent. We charge murder the same, whether it’s committed with a knife or a spoon (apologies for jumping to murder as a comparison, but I like that video).
And really, that’s the other problem. Baseball has never tried to figure out what exactly steroids did. Let’s talk hypothetical-maybe they turn out to be as effective as a corked bat. The last two players suspended for bat corking got eight game suspensions. Steroids already get 50. Most independent studies are struggling to even prove that steroids do what we think they do. You can point to the home runs by Bonds, McGwire, and Sosa as proof, but at the same time, I can point to Neifi Perez or Freddy Galvis or Francisco Cervelli or the dozens of minor leaguers who have tested positive. And at the same time, amphetamines and other stimulants only draw a 25 game ban, and we have links from everyone from Willie Mays to Mickey Mantle to Hank Aaron taking those. A handful of anecdotes aren’t proof of anything. Do steroids help? Maybe. Are they two times worse than amphetamines? Maybe, although it’s even less clear. Are they infinitely worse to justify a lifetime ban? That seems like quite a leap.
Maybe if people began calling for all forms of cheating to automatically draw lifetime bans, I could see it, but that seems both unlikely and overly-harsh.