The 1st Amendment exists to protect individuals from retribution by the government. It does not exist to protect individuals from the consequences imposed by groups who find said speech offensive.
“Since when?”
Since it was written.
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances.
The 1st Amendment restricts Congress from making laws that abridge free speech. The 1st Amendment does not prohibit private organizations from disciplining their voluntary members.