My concern is that you don't open the floodgates to wholesale interference with other cultures. In other words, I'm concerned that there be limitations on what the powerful nations can do to the weaker nations.

Even if ethical relativism does not strictly imply a rule of tolerance or non-interference, there may still be good reasons to adopt a rule of tolerance and non-interference.

For example, in many cases in the past the colonial powers have interfered and harmed other peoples -- destroying traditional industries with imports, reorganizing production for the world market without regard for local needs, breaking up families with new work arrangements such as taking men to work in mines, and outlawing local customs without realizing their utility within the traditional way of life.

I think these are all good reasons to avoid interference.