Of course sugar is fine. the problem is that it is so easy to consume massive amounts of sugar, and most people do. I wouldn't worry about your 2 teaspoons of sugar in coffee. the problem is people guzzling 3 or 4 cans of soda, each with 8 (or even 12) tsp of sugar, then eating other sweets with sugar, then eating a lot of bread, rice, pasta ... The total sum of sugar is then enormous.
Modern man is 200,000 yrs old and we just weren't designed to consume massive amounts of sugar. Keep in mind we've only been processing grains for 5,000 yrs and refined sugar has only been available for 180yrs.