There are a few:
you may have to unlearn a lot of conditioning
you may have to learn how to deal with jealousy
you have to be very honest with yourself and other people
you may have to work on your communication skills
you become a social and sexual deviant in many people's eyes
more lovers mean longer good-byes (it can take you 15 minutes to get out the door)
Most of these disadvantages are also advantages.
What sort of people are polys?
People of different ages, backgrounds and from all walks of life are polyamorous. In general, there seems to be a higher than average representation of people with advanced degrees, science fiction fans, computer and health care professionals, pagans and bisexuals. Some people fall into none of these groups. Polys are a pretty diverse bunch, but there are a few common traits and beliefs.
Common Traits of Poly People:
Not terribly insecure, needy or possessive
Good communication skills
A love of honesty
An uncommon degree of self-knowledge
A high priority for personal growth
They take responsibility for their own happiness
Common Beliefs of Poly Folks:
Strict lifetime monogamy is a myth
People are not property and cannot be owned
People have a right to freedom in their choice of relationships and families
Relationships exist to serve us; not the other way around
No one single person can meet all your needs for an entire lifetime
How do polys feel about monogamy?
Most polys have a "live and let live" attitude. They are happy for those people who have found happiness in monogamous relationships. However, most polys are impressed by the fact that the divorce and adultery statistics indicate that monogamy fails a good deal more than it succeeds.
60% of men and 40% of women have extra-marital affairs.
More than 50% of marriages now end in divorce.
Polys tend to see the modern American nuclear family as an recent aberration in the course of human history and believe that larger, more complex extended families or tribes have been the natural human family structure. Polys frequently believe that children are better off when they have a broad range of adult role models to relate to, instead of a single, monogamously married couple. Polys do tend to object to our culture's idealization of monogamy and suppression of alternative lifestyles.