Terms like 'polyamory', 'group marriage', and 'open relationship' tend to cover quite a lot.
While 'monogamy' usually implies a certain mindset besides being a form of relationship, the terms above are wary about implying anything by default.
As unique individuals, each of the relationships we form are unique as well. Prejudices and assumptions are most often detrimental and misleading.
Approaching an individual with a predefined set of expectations is ignorant at best; insulting at worst.
Even the socially accepted form of monogamy is rarely truly that; most often it serves as a smokescreen to preserving social normality - and thus maintaining social acceptance.
If we discard the assumptions of social normality, to form a functional relationship we are forced to ask some basic questions: Who am I? What do I want? How do I want it?
The answers to these questions are most often fluid and changeable.
Polyamory, as a form of relationship, places the highest value on functionality in regard to the answers and questions above. To achieve this functionality, it stresses a most important tool: communication.
It is a basic observation: if you don't communicate well, the relationship doesn't work well. (The possible causes and reasons for mis-communication are far and many.)
To truly see a person, we first have to remove the thick blinds covering our eyes/hearts.
The closed form of monogamy offers security. What can an open form of relationship offer? A fulfilling lack of security - a chance to replace external security with the responsibility of balance.
And herein lies the danger of openness: if you fail in your balance, you are left without both balance and security.
The choice to decide which are the things worth falling down and getting up again for is left to each of us individually.