Door to door collections

I,ve just had some guy knock on my door from the national deaf society. Basically, he wanted me to set up a direct debit every month to donate a couple of quid or more. No I didn,t sign up. Why? Well whilst I feel desperatly sorry for deaf people, blind people, starving kids in Africa, people with dreadful diseases, people with no legs, animals etc, I simply cannot give to every single charity in the world. So he,s proably gone away thinking I,m right tightfisted old cow. Well maybe so, but do you give to every person who knocks on your door asking for money, or person in the street rattling the collection box?