I wish that posters who don't agree with the OP/myself and other people who've said they don't like this weren't dismissed as some kind of 'Scrooges'. Firstly, it's unkind - secondly, it's inaccurate. I quietly get on with giving to the charities of my choice every single year, without fanfare.
It's not really about 'teens' either. You wouldn't really have toddlers and primary school aged children rocking up to knock on doors for money. If they did however, I'm sure they'd make more effort because from my experience, young children like to give it their 'all' and it's that which makes their efforts endearing. They attract 'givers' when they're in public because they're part of a group, performing and actually, not door-knocking, which many people hate for a variety of reasons.
When was the last time you saw a 'teen', old or young, performing in a group in public, carol singing in town to raise for charity? I haven't - not in recent years anyway. That's fine but WHY do some teens think they have the right to knock on doors? Where is their Christmas spirit, hmm? It's no kind of performance and it's i-n-t-r-u-s-i-v-e. Some people might not mind but there are many who do and we have to put up with the interruption just the same... a bit like cold-callers.
To the parents of said teens who think they are perfectly entitled to 'perform' by door-knocking and screeching/warbling the wrong words to a badly thought out medley of 'tunes' - give your children money YOURSELF. These are YOUR children, not ours.
Lastly, I suppose we all use our own reference points. I spent a good amount of time when I last worked for a council, working with the elderly and imploring them NOT to answer the door as willingly as they seemed to do. It's not that YOUR children are going to cosh them over the head but by frequenting and normalising 'door-knocking' for no legitimate reason, they are, unwittingly, setting up the vulnerable quite nicely for attacks by thugs and thieves who have no conscience about people in society.