IMHO people who try and take potshots against poly are all jealous, sexually frustrated, socially trapped people who are bucking the constraints they feel more than they are attacking polyamory.
America is largely sex-negative and we all suffer under the tyranny of the masses. These anti-poly bloggers are simply jealous that they lack the courage to commit to a sex positive, loving lifestyle.
Every fiber of their being screams in protest. Sex is sinful. Monogamy is the only way. Marriage is sacred. Freaks in bed always rape children. The maintain and defend these beliefs out of sheer ignorance.