Don't define them as a problem species, simply note that there are problems with the species which need to be worked out.
If someone brings up unwanted iguana numbers, mention the number of unwanted cats in a manner which illustrates the responsible attitudes of reptile owners and the ways in which we have managed to curb some of the difficulties inherent in pet ownership of any kind.
By doing so, the idea of legislation that improves the general welfare of animals can be broached as an alternative to bans or restrictions. Rather than not letting anyone have animals of any sort simply because there are some which will be abused and neglected by the ignorant, put the focus on enforcement of existing laws and putting together programs that help ALL animals. If a non-profit reptile group has a fund which donates money to having cats spayed for free, rehabilitating and placing large burms and getting dog vaccinations for owners who can't afford them... Something that goes towards a wide array of educational programs surrounding multiple captive species, it brings other demographics in to support Reptile related causes.
"Genes, Like Leibnitz's monads, have no windows; the higher properties of life are emergent... And once assembled, organisms have no windows." - Edward Wilson, Sociobiology