There are two kinds of friendship:
1. One makes friends based on how one is being treated, in spite of how they treat others.
2. One makes friends based on how they treat others, in spite of how one is being treated oneself.
It can be argued for option 1., that many do make friends based on how those treat others. However, for many, the reason for this is only a measure to determine how they would be subsequently treated themselves.
Consequently, for option 2., the second clause is needed. So that how one is being treated, does not become the measure of friendship.