Nemesis,
As regards your initial question, it certainly does matter! FD mentioned respect and decency earlier and I've got to agree with him...it's clear the individual you mention seeing at local gigs has neither decency nor respect for the suffering of Jane Longhursts' family or friends, or indeed for that of Graham Coutts'.

I'd be interested to know what sort of material this person was performing on stage... and besides, why would a performer need to use a T-shirt to convey a message in the first place...??

Cheers