I too hate these adverts. My husband went to put money into a collection tin and was refused his offer because they wanted him to sign up for a DD, needless to say they got neither.
Although these adverts seem to be worst this Christmas it has been pretty bad for quite some time. About five years ago, in November, I was at Heathrow waiting for a flight and watched as RAF personnel went around to every passenger; no matter their nationalities, religion etc, persistently shaking tins under noses. Watching this spectacle I was embarrassed and ashamed as I felt that we had become a nation of beggars.
I do give to charities of my choice as and when I can afford it but there are charities I no longer give to. The Red Cross because of reasons already mention, and others that demand a certain amount. I also check how much the CEO's salary are, as some earn per year more then my house is worth which took a lifetime to buy, now that does seems very immoral to me.
I think the answer is if you wish to help, pick your Charites careful, check their motives and morals, earnings and don't do DD unless you can afford or wish to do it forever.