Problem with ideal LED diode with much higher voltage than its minimum
Silicon diodes drop about 0.7V.  LEDs are around 1.5 to 3.2V, depending on their color.

If we assume an ideal diode, then if you connect it to an ideal 5V supply, then an infinite current will flow.  Infinite currents are not generally considered a good thing.

In the real World, where no component is ideal, it may go pop, or give off smoke, or just go black inside.  Either way, it won't work for very long.