The ERA is a simple constitutional amendment.
"Section 1. Equality of rights under the law shall not be denied or abridged by the United States or by any State on account of sex.
"Sec. 2. The Congress shall have the power to enforce, by appropriate legislation, the provisions of this article.
"Sec. 3. This amendment shall take effect two years after the date of ratification."
All it means is that women and men are considered equal under the law and that the state and federal governments can't discriminate based on sex. I don't know why anyone would be against the amendment.