The Global Compact For Safe, Orderly and Regular Migration was approved in July by all 193 U.N. member nations except the United States, which pulled out last year.
Hungary quit in July, and on Wednesday Austrian Chancellor Sebastian Kurz said his country would not join either. Poland is considering leaving too.
Arbour, a former U.N. human rights chief, said it was regrettable to see departures because the whole U.N. had managed to find common ground, and Austria - an active participant in the negotiations - should be comfortable with the text and could easily express any reservations that remained.
"What I also find frankly a bit disappointing is that a lot of reasons that are advanced for disengaging are either mistaken or do not reflect what this global compact is all about," Arbour said.
The compact was non-binding and in no way infringed state sovereignty, and suggestions in Austria that it might lead to a "human right to migrate" were unfounded, she said.
"This is coming out of nowhere, it’s nowhere in the document, it’s nowhere on the table."
The compact was a framework for cooperation like the U.N. Sustainable Development Goals (SDGs), a set of targets for improving global well-being by 2030, and it would be "bizarre" for countries to declare they were ditching that agreement, she said.
The impetus for the compact came after Europe's biggest influx of refugees and migrants since World War Two triggered fear of foreigners and nationalist tensions.
Arbour said the compact did not affect states' rights to manage their borders, but simply sought to instil order into cross-border movements.
"One of its main objectives is to reduce, if not to eliminate altogether, unsafe, chaotic, illegal poorly managed migration, which is in nobody’s interest - not the migrants, not the host communities, not the countries of origin," she said.
"So it’s not that migration is a good thing or a bad thing. It’s a thing that’s been with us forever, and cross-border human mobility will be forever with us, but currently some of its poorly managed aspects are a source of genuine concern." (Reporting by Tom Miles Editing by James Dalgleish)
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