What an unhelpful bunch of responses! Although I agree newspapers are not a good source of scientific info, some suggestions of where you
should look would have been nice.
The guardian article is interesting but doesn't answer your question. Firstly, sugars are a huge group of chemicals, with widely varying effects. The dietary sugars we most encounter - sucrose, fructose, glucose, etc. - are generally known to cause harm if consumed in large quantities consistently over time. Diabetes, for example, and various types of heart disease are known to result directly from high-refined-sucrose diets. Not to mention obesity. Of course, the thresholds for 'high' are important.
The place to look for information is the scientific literature. That's not necessarily as scary as it sounds. My first google scholar search gave these interesting results:
Dietary sugars: a fat difference (summary: it's ba-ad)
Dietary Sugars Intake and Cardiovascular Health (summary: bad bad bad, limit your daily intake)
and the related news article...
AHA recommends reduced intake of added sugars
Associations between dietary added sugar intake and micronutrient intake: a systematic review (summary: high dietary sugar may be associated with lower micronutrient uptake, but studies to far have been poorly conducted)
Added sugar and sugar-sweetened foods and beverages and the risk of pancreatic cancer (summary: no support for suggestion of link between high sugar and pancreatic cancer)
Effects of sugar intake on body weight: a review (summary: sugar makes you fat, artificial sweeteners seem to be better, but as usual, we need more data)