As DMcG (no relation) pointed out, there are lot of very practical advantages to getting married if you are intending to spend your life with someone. Civil Partnership in the UK, if the partner is the same sex as you, carry the same advantages.

If it is argued that the term "marriage" needs to be widened to include Civil Partnerships, would the next logical demand be for everyone to abandon the terms "husband" and "wife" in favour of "partner" - or maybe "spouse" to avoid confusion?