I've done this a very few times, always based on a risk assessment when we are at the hotel.
I did it at a hotel near Dover where we put the children to bed in an annex to the hotel while we had dinner in the main restaurant. I checked that the baby listener worked in range (DH went to teh room and whispered and moved around while I checked I could hear), that there was a smoke alarm, that the patio doors were bolted and that access to teh building was restricted (only us and the couple we were with were staying in the annex). Happily had dinner with baby listener on, and we physically checked every 30mins or so.
I did it in a hotel where there was baby listening on reception. Again there was a smoke alarm and we checked that the receptionists listened in regularly (in fact a red light flashed on the baby listening device above the room number if there was any noise from the room) and we took a baby listener (which worked) to the restaurant too.
We did it in a very secluded country house hotel in Scotland twice, where the baby listened worked well and there was a smoke alarm in the room. As it was the hotel we married at and we were on our anniversary on both occasions the hotel staff physically checked for us every 15mins too, and came back and reported in to us when they had done so!
Probably more telling are the occasion where we haven't done it. All of these have been overseas, and the main reason in almost every case has been that there was a swimming pool between where we would have eaten and the room.
In any event, we have always done a long siesta (better for marital relations than dinner together, I suspect and taking the children with us to dinner. The back to room and drinks on the balcony/veranda while the children are in bed. We usually try for around 2 adult dinners a week on holiday though, (usually because we holiday in August when we have a birthday and an anniversary to celebrate) and we book a babysitter for these nights.
The last time we went to Mauritius there was a children's club in the evening and we let the children go from dinner to the club if they wished by themselves. We took the view that there was ample security staff on site and they were with some older children. On other nights all the children played on teh beach together where they were withing sight of us in teh restaurant.
This is a very long-winded way of saying that we have always done a risk assessment of sorts before deciding whether to leave the children in the hotel room alone. As I imagine the McCanns also did. Risk profiles vary from person to person, fo course, and what I would be comfortable with the next person wouldn;t be.
That doesn't make them a 'disgrace', it doesn't make them a bad parent, it is just a different assessment of risk.
There are no absolutes in parenting except in the minds of the narrow-minded, imvho!