> Say the government set up booths in a mall for public officials to make speeches. Could the government then kick out people who bring in pro-abortion signs to such a speech? Probably not.

I am not an expert on this area of law, but it's possible that they could:

https://en.wikipedia.org/wiki/Free_speech_zone

> The existence of free speech zones is based on U.S. court decisions stipulating that the government may regulate the time, place, and manner – but not content – of expression.