It took a lot of guts, brains and talent for a network television show to tackle gay people and gay rights in the early 1970s.
In the previous decades their had been few openly gay characters (much less actors) on television mostly based on cultural cues, sexual innuendos and various gender-based stereotypes. Even less was said about the issue of gay rights. While their was a gay rights movement in post-war America, television -- especially entertainment -- generally avoided the issue.
Hence, this episode was a controversial at the time. It challenged not just homophobia, but larger issues of sexism. Entirely appropriate for the series, but not without some protest.
For example, President Nixon went on record as being very opposed to it and homosexuality in general. Yet, the series would tackle sexuality based prejudice and discrimination in future episodes.
It is a great episode, albeit somewhat dated, and many of the issues raised are still being debated today.