There is a huge difference between "you're pretty and that's the only thing I know about you, want to go on a date?" And "Hey, we share a few similar interests and you are pleasant to talk to, and attractive, would you like to go on a date?"

You should have a baseline beyond simply looking at them. A date is where you get to know them beyond that baseline. If it's a stranger, it isn't unreasonable to say you should have at least a few minutes of conversation before asking them out.