I think I'd be very suspicious and sceptical and, to be honest... I don't think you should offer to buy anyone an ice-cream AT ALL.

I think you have a good heart and are a nice person, but most people might think it is very creepy and you could come across badly through no fault of your own. It's just the nature of people I guess.

Why don't you try and do some volunteer work in your local community or something if you want to do something good? That way your best efforts could actually be seen by people with their own eyes. Thats the way to go I think!