Hi Trine,
I´m not a sociologist or psychologist. I hope you find one.
Interesting points you raise. I´m not convinced that brutalism is a reaction to Thatcherism. Edward Bond´s Saved, which so influenced Sarah Kane is from the time of The Beatles and the rise of the modern Labour Party (conversely also of Vietnam). Its imagery of the baby being stoned to death is as shocking, and theatrically powerfull, as Blasted. Going further back, Ibsen´s Ghosts was described as "a dirty deed done in public", very similar to the reaction to Blasted. The most powerful anti Thatcher play is, in my opinion, Caryl Churchill´s sublime Top Girls which does not use brutalism.
Why use extreme violence on stage? Shakespeare had Lear blinded and in Titus Andronicus there are various amputations etc. But I doubt the audience were too shocked, with bear baiting nearby. It was different when Sarah Kane wrote Blasted. Perhaps she, and others, thought British theatre had become too complacent. The "talking heads" and "chattering" of Alan Bennett and Alan Ayckbourn were worthy but lacked excitement. Just as the blast in Blasted tears the stage apart, I think she wanted to do the same to theatre, and open up new directions.
Iain