I agree (I'm from Ireland, and we're generally fairly pro-EU). Being an island though, the reality it doesn't make a huge difference to us day-to-day.
The way I'd imagine the UK retaining it's opt-out here, is that it's something that the EU could compromise on without really losing much (and importantly without losing face, as the Irish border and preservation of the GFA is a reasonable excuse to find reason to compromise) and that the UK negotiators could then present as a "win" back home, making the other conditions that the UK now has to accept (for example the euro) easier to sell the general populace on.
Obviously though, I'd much prefer if both the UK and Ireland joined Schengen together.
