Hum. I mean I don't condone conducting illegal activities over encrypted chats of course (particularly given than some activities quoted in this article are pretty shocking and would cost these banks the loss of customers), but we should also keep in mind what regulators and compliance departments do with this monitoring of conversations.
The best example is the Fabrice Tourre affair at Goldman Sachs. Two examples I noted:
First the SEC quotes Tourre "More and more leverage in the system, The whole building is about to collapse anytime now…Only potential survivor, the fabulous Fab[rice Tourre]…standing in the middle of all these complex, highly leveraged, exotic trades he created without necessarily understanding all of the implications of those monstruosities!!!" [1]
Where the actual sentence was (translating the bits in French): You should take a look at this article... Very insightful... More and more leverage in the system, the whole building is about to collapse anytime. Only potential survivor, the fabulous fab (as Mitch would kindly call me, even though there is nothing fabulous about me, just kindness, altruism and deep love for some gorgeous and super-smart French girl in London), standing in the middle of all these complex, highly leveraged, exotic trades he created without necessarily understanding all the implications of these monstruosities!!! Anyway, not feeling too guilty about this, the real purpose of my job is to make capital markets more efficient and ultimately provide the US consumer with more efficient ways to leverage and finance himself, etc [2]
I wouldn't write that in an email, but still, the sentence has a very different meaning with the bits edited out by the SEC back in.
Second example, one of Tourre's managers was quoted writing "boy that timeberwof was one shitty deal". This was repeated over and over by congress as if it was a reference to the quality of the collateral of the transaction, i.e. Goldman Sachs sells some product to a client that they call internally a shitty product. But if you look at the actual email trail [3], they are not discussing about the quality of the collateral in that CDO, but of the fact that they are left with a $300m unsold position, which understandably is undesirable as a market maker.
So here we have examples of compliance departments sending unrelated personal emails to the regulators (in a shameless attempt to scapegoat an employee) and regulators editing sentences to alter or ignore the context. No wonder why bankers aren't keen to have their conversations on record.
[1] https://www.sec.gov/litigation/complaints/2010/comp-pr2010-5... page 7
[2] http://i.telegraph.co.uk/multimedia/archive/01623/Fabrice_To...
[3] https://www.hsgac.senate.gov/imo/media/doc/Financial_Crisis/... page 224