I am normally relaxed about idioms but the phrase 'I'm sorry, but' followed by an opposing view to an earlier comment really annoys me and I have just read it in three threads in succession. It makes no sense - why would you be sorry for disagreeing with someone? The whole point of a forum is to debate and discuss so why on earth apologise for politely expressing a different opinion?
A very wise friend says that 'but' is shorthand for 'ignore everything else I've just said and start listening now' and that is particularly true when it is used online. Cast aside the 'I'm sorry' MNetters. State your opinions freely, be proud of your own ideas.
I'm sorry, but that's just how I feel.