In my opinion, if you want to donate, just do it. Don't think about other issues. It will make you feel better knowing that you contribute to something good and it doesn't matter how small it is..I have done this numerous times passing by underpasses where people are busking..or outside mrt stations...just drop a penny or two it won't hurt you much..
Seriously sometimes these people can be richer than you.
There was an old lady in a wheelchair near Somerset MRT quite some time ago, her wheelchair wasn't those kind where she can wheel herself coz the wheels were small and at the bottom. So I concluded that someone actually put her there to beg. And since I used to be there daily, I once caught a glimpse of her bag and inside was a large wad of mixed notes!! Kudos to all the suckers.