Is it technically feasible to "shun" particular bitcoin wallets? Bitcoin is supposed to be an apolitical currency, but the United States reportedly gained some leverage by amassing over 27,000 bitcoins &mdash; and counting. (People seem to be jumping at the possibility of turning bitcoin into the ultimate unmoderated facebook clone and the "content" there is what you'd expect.)

OTOH, this poses a practical problem for the community, because attempting to redeem this amount would probably destroy the currency's market value.

Now, in the marvellous world of atomic hat-based TF2 trading there is a de-facto authority called SteamRep. In short, what they call a scammer is a scammer. Their items become scammed. Trade for scammed items and you become a scammer. This label shuns you from virtually all trading websites, which will be happy to take for themselves whatever items or currency of yours they hold.

I am not advocating for this. I do not have bitcoins. I don't like bitcoins. I also don't like aiding criminals in their trading and money laundering. That's just my opinion and it's worth its weight in electrons.

I do wonder, though, if it would be technically feasible for the bitcoin community to protect itself from a possible sudden devaluation of the currency by marking a bitcoin wallet, and all the individual fractions of bitcoins in there, as "bad, no, worthless, will not accept, will not process transactions" in an attempt to artificially limit their worth.
Not really, if you start doing that then chain forks and a whole load of nasty things follow. There's no real way of blacklisting a "wallet", as by design there's no way of determining exactly the extent of the keys under control by a specific party, so for the sake of this discussion we will assume we have one blacklisted "address".  

Even if nodes reject transactions from specific addresses, miners can still include them in blocks without them even having to be broadcast. If some nodes decide to arbitrarily invalidate blocks with transactions they don't like, you've then got a forked network. Massive double spends occur on both forks by intentional and unintentional parties, and the network collapses in the sea of mistrust. 

Currently, some mining nodes (like mine) specifically refuse to include transactions in blocks that come from known betting site addresses, like SatoshiDice. I however don't reject blocks that contain the transactions, or I'd be very quickly become isolated from the network. 

You'll never get all the miners to agree with any form of blacklisting, so no, it can't technically happen.