What makes you think the discussion is limited to what the law is, versus what it should be, or more broadly, what the 'right' thing to do is, regardless of the law?
Your link does not necessarily refute the post you're replying to. Gay people are not a protected group under Federal law; nor, AIUI, are they in most states.
However, that was not the argument that was made. The original argument is unconditional: "to anyone", period.
The grandparent pointed out this flaw. You are on the same side of the argument.