Hard-Brexiteers would like the UK to have a "clean break" with the EU, and in particular they don't want any part of the UK to stay even temporarily in the customs union (the so-called backstop).
This "clean break" would normally require a hard border between Northern Ireland and the Republic of Ireland, but a hard border would breach the Good Friday Agreement. It seems that the options "the UK leaves the customs union" and "the Good Friday Agreement is upheld" are mutually exclusive.
As far as I'm aware, the only idea that some hard-Brexiteers have proposed to solve this contradiction is a soft border using "seamless technology". Even assuming that such a technological option is feasible for the trade of goods, wouldn't that leave a backdoor wide open for illegal immigration from the EU to the UK? If yes, are hard-Brexiteers ok with that? Alternatively, are there any hard-Brexiteers who support a hard border?
To summarize, what do hard-Brexiteers see as the ideal outcome for the Irish border in the long term?