That's just a bad idea because you're banning more pokemon.
The optimal metagame has been defined (I think) to be the one with the least amount of bans; thus if you ban Drizzle you only make one Pokemon useless - Politoed. Otherwise, you can just use Rain Ludicolo or something and run Rain Dance on a few Pokemon to get up rain. Sure it neuters it a bit but it's far from crap.
Likewise I'm not too sure on the optimal meta's definition. Anyway, I see what you say entirely, but without perma-rain many pokemon are suddenly made unviable in OU. For instance - if Drizzle is banned then Dory and Sun will still exist, meaning teams will probably rarely run Rain, the only perma weather, as setting it up simply gives your opponent too much free momentum. In Gen 4 yes Rain was a very good playstyle without Drizzle in OU, but the presence of Sun now as well as much improved Sand means that it will be incredibly tough for Rain Dance teams to keep up once the other weathers in the meta catch on and begin running a secondary weather user.
Without Drizzle and presuming Rain Dance teams' inferiority to Sun and Sand, Kabutops is relegated to being an inferior SDer with Aqua Jet, Ludicolo a Subseeder with an interesting type, Politoed to a useless NU (as are Floatzel, Gorebyss, Qwilfish etc). Only Kingdra and Manaphy (if unbanned) still have a solid pace in OU. Moreover is the elimination of the Rain playstyle as a whole that I believe will occur if it is forced to use Damp Rocks and Rain Dance in an environment with TTar, Hippo and Tales, which I see as unecessary and detrimantal to the diversity of the metagame.
Essentially I admit that this way means more bans, but overall I feel it offers more diversity to the meta as a whole, countering out the bans which would be made.
http://www.smogon.com/dp/pokemon/ludicolo
http://www.smogon.com/dp/pokemon/kabutops
Both of these have non rain sets.
And anyway, let's use logic.
It is much better to ban the pokemon with drizzle. I am sure that most people would not mind facing rain dance teams, as opposed to a infinite rain team. In Gen 4, there were rain teams, before drizzle was released. People used damp rocks.
Banning the abusers is illogical, because you're essentially banishing pokemon that have non-rain abuse SIMPLY because they have Swift Swim as their ability. Does that make luvdisc uber? Is Phione uber because it has hydration? No. Ban the ability that breaks the metagame.
Indeed they do have non-rain sets for OU, but go look at the usage stats for them near the end of Gen 4 and I think you'll see what I meant by them being rarely used and as such not very viable in OU. If they were so viable then surely they would have been OUs by statistic.
The problem with people not minding facing Damp Rock teams is that yeah, they wouldn't, but it seems Doryuzuu and Sun would instead become much more problematic as their main rival weather can no longer set up instaweather by merely switching in. Comparison to Gen 4 where Rain Dance teams were viable in OU is somewhat tricky given the new Sand abuse abilities and Ninetales (and improved Growth) also being present.
Banning pokemon for their ability is exactly what I propose not to do, however. I don't want to ban swift swim at all, but banning a pokemon for a broken feature (possibly being an ability) is not a foreign or so terrible concept. Part of why Chomp was banned was that Sand Veil made even 100% counters to him into 80% ones (admittedly a tenuous example, but it shows than an ability can be a reason for a ban). Wobuffett even more so.
In any case, would anyone use say Kabutops in OU with its ability Shell Armour? Banning a pokemon because it is amazing in one weather when that is its primary role in OU isn't damaging its other prospects too much. Kingdra is quite admittedly an exception, but the point stands. If a pokemon can run non-broken sets and broken sets, then we do not solely ban the broken set from use, we ban the whole pokemon. This is not picking on swift swimmers or anything of the like.