Fruit is good in moderation. It does spike blood sugar and if a person is trying to lose weight, fruit is not always the best choice. Berries in moderation are ok though. Fruit contains fructose, a natural sugar, which is far and away healthier than refined sugars.
Along with this the processed fruit juices are all unhealthy and most of them are loaded with extra (refined) sugars. Refined Sugar is just bad for us generally.
But people have been eating fruit for thousands of years, as you might realize. However, before the advent of grocery stores and importing fruits and other foods, people had to forage for their own food. So they only got fruits when they could find it, and this was usually end of summer and in fall. So they packed on a little weight which was helpful for them to get through winter. Most people couldn't find fruits year around.