It seems to me that you assume that by saying
"one has no obligations whatsoever toward the people one deals with"
one is also saying
"... therefore, one can do whatever one wants".
I do not think that way though, nor am I advocating it in any way.
I believe it is possible to act responsibly also due to other intentions, not only out of "regard for others".
That is, two people might have performed similar actions with similar results - but they could have done them with completely different intentions.
One did it "out of regard for others" and the other did it "because they believed it was the right thing to do".
"Regard for others" can be an external description of an action, but "regard for others" can also be an intention that a person can act on.
Many times, the intention of "regard for others" comes out really badly - you probably know of the terrible things that happen sometimes when a person seeks to help another, but only makes everything worse.
In short, having the intention of "regard for others" does not necessarily lead to actions that can be described as "regard for others".
On the other hand, a person's actions can be described as "regard for others", even though the person had no intention of "regard for others" while perfoming those actions. Take for example doctors who are just trying to do their work right - it comes out good, but they don't even know the patient's name.
In short, actions that can be described as "regard for others", are not necessarily performed with the intention of "regard for others".