My view is that allowing gay marriage is itself a consequence (probably unintended but still welcome) of other radical changes to the institution of marriage in

My view is that allowing gay marriage is itself a consequence (probably unintended but still welcome) of other radical changes to the institution of marriage in Western society in the last century or two. Such changes include the view of a marriage as a personal unit rather than an economic one united by love rather than mutual economic and social benefit, and the general increase of women's rights and convergence of gender roles (for example, women can own property, and are not treated as being property themselves). The whole "soulmate" thing is a relatively recent idea, but is the current ideal for marriage. We have thousand of years of experience with a variety of institutions that share the name "marriage" but aren't very similar to each other. The current institution that bears that name has arguably only been around for about forty years, most recently being re-written by the sexual revolution and the increasing social acceptance of divorcing and re-marrying. Considering how flexible we as a society have become with respect to gender roles, this change is hardly "radical" by comparison.