It's not unusual for a museum to have this sort of alchohol licence - I am not sure what the hoo-haa is?

I really doubt they will be going down the cheap and cheerful lager route. They will be wanting to bring in extra income, and as Government is no longer guaranteeing funding for national museums after 2015, they are under even more pressure (you may remember discussions on this forum about the future of the Horniman following withdrawal of Gvt funding see http://www.se23.com/forum/showthread.php?tid=3715). DCMS at the time said museums are the responsibility of their local Council and community. We are that community!
So the museum governing body would be looking for other ways to bring in income. They will be looking to attract visitors who will spend more per head. I would say this application is a wise move on their part. Maybe the residents who object so much to the museum selling alcohol and running occasional large events would like to do some fundraising for the museum instead (apologies if you already do) although an occasional craft fair, worthy as it is, is really not going to fill up those coffers.

I used to work at one of the larger art museums in the centre of London. The cafe and restaurant were a huge source of income; they sold alchohol and there was never a problem with drunken behaviour, apart from the staff ;-) (that was a joke, before anyone gets panicked about hordes of drunken Horniman staff wandering the gardens at night).
It was mainly purchased by people having a glass of wine with their lunch. Come on, if someone wants to get drunk do you really think they will buy an overpriced bottle of wine from a museum cafe, or go down the road to Tesco where they can get a bottle of cheap plonk for a fraction of the price?

The other big source of income for museums is sponsors - who usually expect as part of their sponsorship package the option to run well-catered functions, which would have to include alcohol, and might run late, but would certainly not be particularly noisy or disturb residents.

I like living in Forest Hill because its not too suburban; it is leafy with nice houses, and lots of families and friendly people, yet the proximity to the centre of London gives it a bit of an edge and makes me feel like haven't disappeared into the sticks. However I sometimes get the feeling reading SE23.com that some of the residents wish us to become more suburban, not less....

:-)