Given that we, as humans, have a natural sweet tooth it's not surprising that the most common recommendations for non-rum drinkers are Zacapa 23, Diplomatico Reserva Exclusiva and El Dorado 12, all sweeter rums. From the lists circulated these three all have significant amounts of sugar added to them (up to 45 grams per litre).
Why this matters
Sugar covers a multitude of sins, a man after my own heart has undertaken an experiment to see how adding sugar changes the flavour profile of a simple white rum (Havana Blanco). The conclusion was that small amounts smoothed the edges off and made it more drinkable while larger amounts gave an impression of longer ageing.
So you can see that you could , if you were of a nefarious mindset, take a low quality spirit and add sugar to pass it off as something more refined and charge accordingly. I'm NOT suggesting anyone is doing that but I can understand the concern.
From my point of view this is similar to the addition of caramel and chill-filtering of Whisky, does adding sugar make for a bad rum? No, obviously not, there are bad rums with no added sugar and good rums with it and vice versa. Rum is an expression of the quality of ingredients and the care taken to produce it, I am certainly on the fence as to adding sugar, I can see the value in disclosing it but I'll certainly still be drinking a glass of El Dorado 12 later.
I'd recommend two articles from the floating rum shack, one from Alexandre Gabriel of Plantation rums making the case that added sugar is not a big deal and one from Richard Seale of Foursquare arguing that it is.
Both articles come from their own commercial positions. Gabriel is a cognac blender and as such the addition of sugar to spirit as part of the blending process is a natural step and a skill, he argues that, like salt, sugar is a natural flavour enhancer in small quantities. Seale, as a Barbadian rum producer is barred by law from adding sugar, distillers in Barbados, Jamaica and Martinique are forbidden from adding flavour enhancers.