Those people are being ridiculous then, given that UK CPs don't have any legal recognition in much of the world. That proposal would place UK residents in a position where they have no domestic access to the only legal contract that will afford state recognition of their partner relationships anywhere they travel. This protection would be limited to those who have the money and wherewithal to organise it internationally (and please nobody try and suggest that if you can manage a package holiday somewhere there'll be no barriers to you arranging a marriage contract abroad too).
It is a genuinely appalling idea, and not at all comparable to abolishing CP full stop. Which was at least practically doable, whatever one might feel about the fairness and desirability of it.