Cross border workers, trade, transport, politics etc.Huge negative for who? People are illegally entering this country on a known route using a known mode of transport. There are regular Garda checkpoints at the border checking for other things, this would be no different.
Putting a formal checkpoint border on the island of Ireland (Pre-Good Friday Agreement) to try to stem the flow of asylum seekers would only go down well with the Unionists and Brits.