I personally gave up on band t-shirts about 15 years ago. The last I wore was a Beastie Boys one - a rather fetching baby-blue colour, basketball logo on the front.
You could get into a whole discussion about visible identifiers of musical preferences - from lapel badges (still got my "two fingers up to you" SLF one), the steam-pressed lettering that people put on their Harringtons in the late 70s (remember that?), band names on school rough books, etc. Even walking back to the bus stop from the record library has been known to involve complicated judgements about which record to leave visible on the outside as you carry them ("hmm, shall I put the Gene Loves Jezebel one there, or The Marine Girls?")
Back to t-shirts. When it comes down to it, I'm a non-wearer. Of any t-shirts. To me they look like a child's item of clothing. Hey, if you want to look like a three-year-old why not wear some baggy shorts and dinky, colourful trainers? (ah, too late, thousands of 45-year-old men are already at it ....). So I tend to think that emblazoning a band name on the front of this ensemble hardly redeems it.
Also, how imaginative/creative is it, anyway, to don a top with someone else's band written on the front? Kind of clone-like. (It must be awkward, by the way, to bump into someone at a bar or gig who's wearing a t-shirt that exactly mirrors yours. "What kind of music are you into ...?").
No, band t-shirts are a little too like replica football shirts. Essentially, overpriced tat drained of imagination.
It also goes without saying that t-shirts are a convenient way to fleece the punters while getting them to act as a walking advertisement for the band-as-brand. Hey, it's a win-win. That's why I always liked the (mildly) subversive gesture of John Lydon's, with his "I hate" addition to a Pink Floyd t-shirt (better still was the "I hate" Rich Kids one he did). Similarly, I think putting rips and whatnot into t-shirts, a la punk, at least showed some spirit.
Meanwhile I think the outrage of veteran punks over rich celebrities wearing Crass t-shirts is petty and misplaced. If Angelina Jolie wants to be papped in a Crass top, so what? If David Beckham thinks it's cool to strut his stuff in a diamante-studded Crass t-shirt, then let him. Penny Rimbaud doesn't like it, but at least he's sensible enough to denounce Beckham in a half-serious, half-humorous way. There's nothing sacrosanct about Crass products ("we are all products" etc) and, while I like their music and much of their political stance, Crass fans - and former band members - ought to adhere to the Anarchism-influenced principle that people should be free to wear whatever they want.
In fact, as it happens, I can't help thinking that Beckham's luxury Crass shirt is a bizarre but brilliantly decadent move. If you're going to go around in a band t-shirt, at least do it with a little flair.