Sorry, I also agree with Joel here. If the twatty audience members hadn't mentioned that This Morning said singing along was alright, he might have been a bit OTT in his response but they were literally using This Morning to justify their appalling behaviour.
I've worked in theatres and fully support the recent drive to bring etiquette to audience members. The level of drinking, entitlement and disrespect to staff, performers and fellow audience members is unacceptable and it's HEINOUS* for a TV show to endorse singing along at the theatre. You just don't unless you're told you can.
*sorry, had to Carrie for a second there