There is no negative definition of monogamy. There are only negative attributes and behaviors associated with some of it's participants. Possessiveness, ownership, control, insecurity and fear are all attributes of some individuals and should not be considered a quality of the way a body of people love. The same application of negative attributes in regards to polyamory are exploited by those who are afraid of it or don't understand it. Slutty, fear of responsibility, immaturity, inability to commit, sexually unhealthy are not the qualities of the entire poly community but they are the attributes of some of it's participants. Again, to blanket the whole community with the negative attributes of a few is to do a whole body of people an injustice.
Monogamy is the achievement of intimate completion through the sharing of energy and sexuality with one person. If that is how you work, it is a wonderful and peaceful place that gives you confidence and strength to take on challenges in other areas of your life knowing that at least one part of it is solid and constant.
That's my monogamy