Freedom of speech is a huge, complex issue, and ironically, in atheist environments, I'm usually arguing the other side. I'm not particularly offended when a business leader pays to put up a nativity scene in a public park. I might not like the nativity scene, but I don't see it as infringing on the rights or safety of members of communities that do not share the beliefs of those who put it there. But the law usually prefers to protect those groups and individuals, and in fact prohibits the freedom of speech of that private investor who wants to put up a nativity scene. You would fight to support the rights of the private investor who wants to portray the virgin birth?
I can't speak for HAL, but if the business leader were paying to put the nativity scene in a public place that was
(a) permanently designated for private expressions or advertisements and
(b) open to any group for such expressions for the same fee
then yes I would, as an agnostic atheist anti-theist who supports freedom speech of expression, support their equal access. I would do so in the same way that I would support a gay art statuette, a tribute to the KKK, or a memorial display for Ted Bundy.
Nativity displays are not analogous to the subway advertisement scenario because public places that allow nativity displays typically don't afford that forum to others with dissenting views.
So you are arguing that there should be NO RESTRICTIONS on free speech. You would have no concerns about a private investor putting up signs in a public court house, stating that one ethnic group was more dangerous than another? You would not have problems with a public school displaying a sign by the private sponsor who paid for the new gymnasium, stating that some students are intellectually superior to others, based on their cultural traditions?
Similar problem as above: When a private sponsor funds the building of a public facility the facility does not magically become privately owned and thus a blank slate for said sponsors views. Any much more than a "Sponsored by..." or "A special thanks to..." is fairly rare I think. If, however, the public place has a sounding board that sells space that is equally available
to people with differing views then yes, that should be allowed.
If the NYC board of transportation, and by extension the people of NYC, do not want certain speech on private advertisements in their subways then they have an option: remove private advertisements from their walls. If they choose to keep accepting money from people wishing to advertise on said walls then they should not have the authority to censor certain opinions.
The correct response to bad speech is more speech, not vandalism, theft, or censorship.