Most Helpful Girl
The negativity might be for a few different reasons, there's dodgy characters about so they might simply not like the idea just because they're just looking out for their own safety, asking a girl out on the spot like that can make them question your intentions, you have shown interest in a very forth right manner and this can be intimidating to some women.
Some guys find it easier to be straight and up front and do that and some find it easier to go slowly with someone they're fond of, I think the second option works best either way. It's nice for women to know you're interested if you show consistent interest and THEN ask her if she would like coffee, it shows respect for her space and time. Asking a girl immediately without really knowing her might make her feel you're slightly desperate and that would lead her to question your motives and you as a person.
Be brave, slow and steady wins the race ;)