It sounds like the editorial writer is arguing that good people are good voluntarily (so the law doesn't affect them), and bad people will use this law as an excuse to be worse. A lot of the consequences this writer sees arising from the law are things that already happen (have you ever searched for a job while pregnant?), which there are already anti-discrimination laws in place to try to prevent.
The editorial is arguing that less law is better than more law, which may be a defendable position, but me, I like the protection for breastfeeding women. The women employed by understanding employers tend to be higher up the socioeconomic ladder than average, and lower down, things are much harder. A law may allow individual managers to do better by employees even in the face of pressure to focus on the bottom line. The law is a little vague, but if it was more precise, I'm not sure it would be better. The law gives women something to fall back on when and if their employers are jerks.
I also think the writer missed some possible worst-case scenarios, like breastfeeding woman gets mastitis, misses days of work, gets fired for using "too much" sick time. How many of us have *any* sick time left after returning from maternity leave anyway?
The United States is a culture that fetishizes babies while providing no support to the people raising them. If the capitalist system is going to tell us (as it does) that we *should* have babies, and that we had better raise them without any kind of public assistance, the least the law can do is defend women who are doing their best to do just that.