It seems that for half the people on HN the conversation immediately stops with "this is about civil rights, therefore we should not tolerate Eich's intolerance".
But marriage itself is not a civil right. It is a pact between two people, a type of contract that we have inherited through a long series of civilizations, to which the modern state associates a number of privileges.
Right off the bat, if we consider any of these privileges a matter of equality before the law, then it is the institution of marriage itself that is discriminatory. Why should an unmarried person pay more taxes than a married person for the same income? Why cannot they name a friend instead of a spouse as a dependent for health insurance? And so on. How is it acceptable to discriminate against people who are not in a romantic relationship? Why are we tolerating this obvious injustice?
The answer is that, traditionally, these have not been seen as rights, but as privileges. The state grants these privileges to married people, at a cost for the community, because these is believed to be a public interest in the promotion of marriage. If that is the case, it is entirely legitimate to debate whether this public interest exists both in the case of heterosexual and homosexual couples, and furthermore, whether it still applies to anyone at all in modern society. A lot of the traditional justifications for public support of marriage were based on strongly differentiated gender roles, and it should be clear that they are no longer applicable.
As for new rationales of public interest, none have been advanced, other than "discrimination" - which, again, would be an argument for abolishing marriage, not for extending it.
In any case, this is a matter on which there is ample room for debate amongst well-intentioned and rational people. It is not right to nip the discussion in the bud by framing anyone who holds a different opinion as a bigot.