The fiber is whole fruit makes it much safer to consume. There are dietary exceptions, but sugar alone has 0 nutrients and causes unhealthy spikes in blood sugar (this includes fruit juice). The fiber in whole fruit helps smooth things out. Studies have been completed to test very high whole fruit consumption. I'll let you look them up because I get flamed every time I post a source because .... The Internet. The funny anecdote from these "super high fruit consumption studies" were massive, massive poos.

This is a good, overview on the concept: http://time.com/5301984/can-you-eat-too-much-fruit/

Edit: Other commentators posted great resources.