Do you really believe the government has no constitutional power to end the war against women in the workplace?
It's time to get back to basics here. The First Amendment prohibition on government censorship is based on the "free marketplace of ideas." The theory is that the best way to deal with harmful or false speech is not to suppress it, but to counter it with more speech. This laissez faire approach was designed primarily for public settings where energetic debate is possible.
But most workplaces aren't like that. Employers have a total monopoly over what speech is allowed on the job. Usually, you have two choices: Say things your employer will tolerate, or risk being fired. Hardly a "free market" of expression.
Can the government step in and break up this monopoly to promote equality? When you answer "no," you're not helping workers gain more freedom to say what they choose. You're promoting absolute censorship power for employers, which they have long exercised in favor of intolerance and against equality.
You claim that the government may protect captive audiences only in "public" places. But our society has moved away from the public/private distinction, in part because of the severe harm it inflicted on women. For centuries, men were permitted to beat their wives (sometimes even to death) without fear of criminal prosecution, because the home was regarded as a private sphere untouchable by the government. The Supreme Court has moved beyond this dividing line, and upheld restrictions on expression in areas like obscenity, defamation, and "fighting words" in both public and private contexts. (The court opinions in the bus-advertisement and abortion-clinic cases, for example, do not restrict their principles to public contexts).
One example you mention to support a return to this distinction is your desire to preserve the right of "[p]rivate commercial landlords [to] refuse to rent to the Communists or the Nazis." But do you also believe that landlords should be permitted to refuse to rent or sell property to African-Americans? Disabled people? Women?
More than 30 years ago, Americans decided they didn't want to live in a society that tolerated these forms of discrimination, public or private. And we stopped it with the best weapon we had--enactment of the Civil Rights Act of 1964 (which, among other things, created a legal framework for protection from workplace harassment).
You're concerned about the broad impact of sexual-harassment law because "every place is someone's workplace." Of course, this isn't strictly true (no one's employed in my home, for example). But more to the point, sexual-harassment law doesn't mandate suppression of abusive gender- or race-based speech in any workplace, even when it's pervasive. All it requires an employer to do is take action that is "reasonably calculated to end the harassment."
Consider a female park employee who complains that she's suffering discriminatory harm because she's forced to patrol an area where a group of male supremacists congregate on a daily basis, shouting slogans about female intellectual, physical, and spiritual inferiority. One option for the park manager is simply to change her assignment. Nothing more, nothing less.
You propose a dividing line that protects potentially harassing speech when it is made to willing listeners, but restricts it when directed at a recipient who "doesn't want to hear it." But that line is already built into harassment law. No liability may be imposed unless a plaintiff proves that the harassment was "unwelcome" to her--and proves that after she communicated this fact to the harasser, he continued anyway.
You worry that if we restrict workplace speech in the name of equality, we're starting down a slippery slope that will allow similar restrictions in the name of anti-communism, the nation's war powers, and "protecting police officers' lives" against pro-violence rap music. I share your concern about these and many other values being invoked to restrict speech. But the principle of equality is special. Nowhere does the Constitution mention protecting police officers from harm or containing the spread of communism. It does mention protecting equality.
The civil-rights amendments, passed in the aftermath of the war against slavery, specifically empower the government to prevent discrimination on the basis of race and gender. The senator who introduced the 14th Amendment described the Equal Protection Clause as a "direct affirmative delegation of power to Congress ... [that] casts upon Congress the responsibility of seeing to it, for the future, that [the constitutional mandate of equality under the law] is carried out in good faith." Federal law prohibiting sexual harassment does just that.