Why would advertisers want their ads to run next to content they don't support? Free speech means they are free not to advertise if they don't like the content.

Why would advertisers want their ads to run next to content they don't support? Free speech means they are free not to advertise if they don't like the content. Facebook is allowed to avoid censoring posts if that's what they want to do, but they don't have a right to advertisers' money.