Here's how Ricky Gervais in the Netflix series "Afterlife" dealt with two punks demanding money:
Of course I'm not suggesting you smash anyone in the head with a can of dog food, but I can say that I greatly enjoyed watching the series.
I did enjoy the series as well. The thing is the people OP describes are not belicose and rely on pityness to get their money.
Being from a first world country, or looking like you are, will draw some of these people.
Some people knock on my door from time to time and I just tell them I have some food and they're okay with that, some pasta, sugar, etc.
I think the main difference with what some of the posters here are experiencing is linked to some kind of entitlement poor people might feel to some of your wealth, especially being a foreigner.
I think the worst you can do is giving them money; just give them edibles, that way, if they keep coming you know you're helping them and they are indeed going through a rough time and will be happy with something to eat.
There's a guy who appears 4 times a month on my front door and he's happy with what I give him: pasta, coke, some fruits, etc. I may be luckier than most since he's quite grateful and I know I'm helping someone who really needs the help of those who can afford giving away some food.
Regarding the more problematic "beggars" I think telling them that you can give them food or nothing in a firm tone will be your best shot; if the situation escalates avoid confrontation since some of them have nothing to lose, but after seeing you making it clear that it's either food or nothing will discourage them from coming again, or so I hope.
My 240ARS (around 2 USD cents?)