If marriage is slavery, shouldn't it be outlawed?

[Djuna]

Several feminists have said that marriage is a form of slavery. Usually they themselves were unmarried, so I'm not sure that they really had a good grasp on the whole thing. Anyhow, if this is meant in a literal sense, shouldn't marriage be made illegal? Shouldn't feminists become abolitionists? Where are the marches for freedom? Or is it more of a sour grapes kind of issue - those rotten wives may *seem* happy, but really, they're slaves. Single gals are so much freer.

Since marriage constitutes slavery for women, it is clear that the women's movement must concentrate on attacking this institution. Freedom for women cannot be won without the abolition of marriage." (Sheila Cronan).

"The end of the institution of marriage is a necessary condition for the liberation of women. Therefore it is important for us to encourage women to leave their husbands..." -Declaration of Feminism.
These quotes were in the 70's. De Beauvoir was in the 50's, and Germaine Greer wrote in 1970's the Female Eunuch:
"Women's liberation, if it abolishes the patriarchal family, will abolish a necessary substructure of the authoritarian state." She's not really considered a "radical" feminist, by any means.
In 1993, Catherine McKinnon wrote:
"the private is a sphere of battery, marital rape and women's exploited labor." Clearly, this notion of marriage as slavery is not limited to the 70's.