Why do need Sparta need high population of slave?

For the Spartiates (the Hoplite soldiers) at the head of the Spartan society to dedicate their lives to the feats of war, someone has to till the fields, forge the steel and harvest the crops.So for around 10,000 hoplites and their families they enslaved an enormous number of fellow Greeks including the entire population of Messenia after 2 bloody wars.They wanted a utopia to live in, and what better utopia than everybody doing the work for you! In order to keep the massively outnumbering slave population from revolting, young, highly trained Spartan boys ranging from around 13-16 roamed the countryside day or night, killing any helots (slaves) they met along the way. A reign of sheer terror was the underbelly of the Spartiates' utopia.