So I've avoided this thread after like the first few pages, but since I get to vote, I'll post my thoughts.
Shadow Tag: Do Not Ban
The basis of this test is whether or not STag is uncompetitive. Not whether or not its OP. It is the latter, not the former. Uncompetitive in relation to the game of Pokémon is something RNG related that neither player has 100% control of. An example of this is Swagger. Swagger was a move that was heavily RNG reliant that also took things out of the players' hands. Neither player had full control over the situation, but the Swagger user did have an advantage in that using something like Ditto, spamming Substitute, or simply boosting was made exponentially easier whenever the RNG. Decided to say 'fuck you' to the opposing player.
So what does this have to do with STag? It has to do with the fact that STag is not RNG reliant and it does not take control out of either player completely. Yes, a mon is trapped. No, the trapped mon isn't completely useless. Yes, supportceus falls to Taunt Mega Gengar, but it still has the free will to choose which move to use. It doesn't matter if you might die before you even get to use your move. That's just something being OP, not uncompetitive. Ubers is full of OP shit and that has never been the basis for a ban and it shouldn't be now. Most of the pro ban arguments I've skimmed through all lead to tag being OP, rather than uncompetitive.
And just so I don't have to keep defending my point across multiple pages, I'll just explain why tag isn't uncompetitive. As previously mentioned, it is not RNG reliant, and even in its presence both players have free will of choice. Once a mon is trapped, that free will of choice for the trapped mon is still present, even if it is limited. Just because the choice is limited doesn't mean that the choice doesn't exist. I've mainly seen arguments on the pro ban side saying that tag takes away a players choice. It doesn't. It simply limits it. The only true exception is when Gothitelle tricks a choice item onto a mon. Otherwise, that free choice goes from choosing moves and switching, to just choosing moves. As long as that choice remains, competitiveness remains. It's just like how in chess when one person puts the other in check. The other player still gets to make a move. It's just that his move is limited to only being able to protect the king. It's the same principle. The choice is limited, but it exists, therefore leaving at least some element of competitiveness.
Now, I see where the pro ban side is coming from. STag is obviously a big issue, which is something I saw in my endeavors while laddering. Removing something like Poisonceus to make way for a geoxern sweep is really fucking frustrating when all you can do is burn the damn thing while it slowly kills you with Shadow Ball. It's no fun, and its OP as balls. However, this is Ubers, and things should not be banned for being OP / centralizing. That literally goes against the Ubers philosophy. If tag was this big of an issue in OU (which it's not, thankfully), then I'd vote to ban it in a heartbeat. But this is Ubers, and tag is just one of the many OP Threats that plagues this meta. It's definitely high up on the list, but that's pretty much irrelevant when things like CB Ho-Oh, Extremekiller, GeoXern, SpecsOgre, and a whole bunch of other shit run the tier.
So in essence, Shadow Tag isn't uncompetitive like it is Overpowered. Based on OPness alone, it does not warrant a ban and I will be voting as such.