Bans are a stopgap solution.
In an ideal game, we wouldn't want any bans, because every champion would be well-designed and well-balanced (and, at least to a greater extent than today, would be picked more equally.)
Unfortunately, we do not have an ideal game.
A number of champions exist that people simply do not want to have to play against, either because they are simply overpowered, or because their kit is not fun to play against - or often, both.
Suppose that there is a champion who outperforms any other champion in a role - without being able to ban that champion, to optimise your chances of winning you are forced to either play them, or pick a champion that counters them because you know that your enemy will pick them. (Many people still choose to "take the hit" and play a champion that they enjoy, even if it hurts their chances to win, but that's not really relevant to the argument.)
Being able to ban out that champion means that the player is free to choose outside of that small pool. They aren't forced into "I have to pick X, because otherwise the enemy will pick Y and I won't be able to deal with it."
Now, suppose there is a champion who is just extremely unpleasant to play against. They might not tend to win, but everyone hates being forced to deal with them. Maybe their laning phase is oppressive, maybe they force you to build really sub-optimal items to survive them, maybe they force you to pick champions who counter them or be unable to do anything against them.
This champion is probably a lot of fun for the player playing him (after all, they are dominating another player), but should his opponents be forced to play against him constantly, despite hating it? Shouldn't the lost fun of the other players outweigh the fun of the one abusing this champion?
Again, bans come in here to allow players to avoid the champions that they absolutely don't want to play against, those which completely take the fun out of their gaming experience.
The proper solution is to fix these problems - to bring the overpowered champions into line, to rework the champions whose kits are toxic to play against.
This simply hasn't happened.
Instead, the number of "problematic" champions has increased along with the champion roster.
Bans are the temporary solution to bad balance and bad design, and they need to be there until / unless the balance and design can be fixed, the champions nerfed or the toxic kits reworked. As more problems arise, shouldn't there be more bans to help overcome the issue?
Personally, I'd rather see the balance fixed than the number of bans increased, but if that isn't happening, then more bans would be a stopgap solution to avoid the issue and improve the quality of the game experience.
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