Unfortunately, "just use a little sense" may be dangerous advice. Here's a story from earlier this year about a guy who called 911 when he came across an injured person lying in the street. As thanks for his trouble, he was assaulted by police, arrested, and spent twelve hours in jail -- mostly in solitary confinement: https://news.ycombinator.com/item?id=7233730
I think most people either don't realize or choose to ignore the fact that calling the police rarely prevents any crime. It can be effective if what you're seeking is retribution or revenge, but once you've been stabbed whether you heal or not doesn't really depend on whether you answer questions from the police.
The news from Ferguson is a reminder that bringing police into a situation can make many situations much worse for everyone. If I find you bleeding in the street I'll help you get medical care and if you want to go to the police that's your decision, not mine.
This is a somewhat absurd argument because what I'd do ultimately depends on the circumstance. If I truly know nothing besides my own name and that I found this person bleeding, I would be wondering where my other memories went and if I were brain damaged.
In the general case, they aren't going to be sending detectives immediately to ask questions because someone called 911. Nor would I stay on the scene longer than I was medically needed to be there. But the "general case" is a useless fiction.
As far as I know this applies for all questioning, regardless of whether you're free to go, being detained, or under arrest. IANAL but I've had plenty of encounters with police.
The key right you're asserting is not a "right to a lawyer" it's the right to remain silent. Asking for a lawyer helps you to do this, because otherwise they have much more latitude to try to convince or trick you into talking. If you said you are remaining silent until you talk to a lawyer, in theory, they have to leave you alone until the lawyer is there.
If you aren't in custody, they don't have to provide an attorney and they can keep asking questions.
And custody can be fairly broad, for example a traffic stop doesn't count.
If you see some old lady get robbed, that's not coming back on you.
Also, if the police don't put you under custody, you don't get Miranda rights and you don't get the right to a lawyer necessarily. You'd have to pay one yourself.