No, it is not safe. And there are no significant benefits to make up for the impact on your health.
First up, fruit is very high in the sugar fructose. The idea that this is "healthy" fructose compared to the corn-syrup derived fructose found in processed foods is a misconception. The only difference is that when you consume fruit, you are also consuming fiber which slows absorption of the sugar, contributes towards you feeling full and toward bowel health. But if you eat mainly fruit, you will still need to consume a very large amount of high-sugar food before feeling satiated.
Risks associated with high fructose consumption include weight gain, tooth decay, type 2 diabetes, liver disease, pancreatic cancer, metabolic disorders (e.g., Gout), and kidney damage. Again: it doesn't matter where the fructose comes from. It's the same molecule found in fruit as is found in cans of soda.
There are further risks which will depend on how much non-fruit food you eat. Your body is programmed to require a certain level of protein and fat. If you don't eat sufficient amounts, your body will attempt to synthesise them from what nutrients you do have. This is metabolically expensive and will require you to eat even more fruit (with an increase in the risks mentioned above) or you will enter adaptive thermogenesis, an exhausting condition where your body starves you of energy to maintain calories.
There are also risks of nutritional deficiencies. High fruit diets provide low levels of vitamin B12, calcium, vitamin D, iodine and omega-3 fatty acids, which can lead to anemia, tiredness, lethargy, immune system dysfunction and osteoporosis.
In return the chief benefit of a high-fruit diet are the consumption of high levels of anti-oxidants. These reduce the risk of cancer and can help with other long-term illnesses. However, given that the diet can, itself, cause long-term illness it would seem sensible to take a more moderate approach.