Ever so often a polyamorous person may find themselves in a situation where their partner(s) want to date their friends. Some people have no issue with it whatsoever and others are completely against it. They may be so against it that is a part of their boundaries or relationship "rules". It can easily be a non-negotiable for those people.
Is it okay to keep your friends to yourself in polyamory?
It depends...if you see your friends as belonging to you - that can be an issue. They are individuals and have a right to pursue any relationship as long as it is consensual. However, on the same note, you have a right to NOT date someone who would pursue relationships with your friends. Of course it can be framed better than "my partners can't date my friends", but the results are the same: don't date my friend.
Whether or not you agree, it is at least fair to hear someone out on why they hold this stance. Violating this for some people would mean their relationship with you would be at risk of ending as well.
Why would friends be off limits, especially if we are all polyamorous?
If a romantic relationship between a friend and a partner exists there is a chance privacy will be compromised. It can be very difficult to keep certain things confidential especially if someone cares deeply about both people. Some polyamorists would just prefer to avoid this altogether.
Too Close for Comfort
Some people simply do not feel comfortable having those they are close to - close to each other. Not because they are trying to hide anything, but because of the blurring of boundaries and relationship structures. There is also the fear that the relationship may have pressure to transform into something they never wanted
Alternatively, there is a chance when a partner is dating a friend that a potentially manipulative dynamic can be created. Information may pass through people versus directly and two people can "team up" on another person. Even if someone trusts their partner & friend, this is still a possibility.
The Break Up
Some people have experienced the uncomfortable tension raising and explosion of a break up between a friend dating a partner. It is difficult to ignore the pain between the people they care about. Break ups also put them in limbo between the two for maintaining a relationship (platonic or intimate) with the other.