Why don't we apply to the same logic to every potential decision? Many Republican tax cuts have been unprecedented, so (il)logically conservatives should have opposed them. The iPhone is a disruptive technology will have "unknown consequences", so clearly it should be banned.
The reason we don't apply this idea (except to things we already disagree with) is because it's completely illogical. Caution is one thing, but simply dismissing every idea that could have "unknown consequences" is a great way to make sure that literally nothing gets done. It is certainly not rational. It is, in a word, FUD.
It's about as similar to social institutions as marriage is to divorce, which you tried to equate. Probably more similar, actually, since marriage and divorce are opposites while communication is a keystone of society that's intimately involved in most of its institutions.
At any rate, saying America's current implementation of marriage is a social institution going back through all of history and geography is just plain weird. Even in the modern age, marriage means very different things to different cultures, and that's ignoring all the "marriage" constructs that have existed in the past. Outlawing polygamy was a greater offense to the history of marriage than allowing gays to marry.
The reason we don't apply this idea (except to things we already disagree with) is because it's completely illogical. Caution is one thing, but simply dismissing every idea that could have "unknown consequences" is a great way to make sure that literally nothing gets done. It is certainly not rational. It is, in a word, FUD.