Sex is extremely important for a healthy life. Even Maslow placed sex among other physiological needs such as food and water. So it's THAT important of a need.
Also as explained by Maslow, Humans need feelings of belongingness. Like intimacy and friendship. Not having any sex reduces your chances of satisfying these needs as well. Incels are hated by society because we can't get sex therefore we have low self esteem and can't satisfy our belongnigness needs.
So when someone tells you that sex isn't a necessity, You should tell them to shut the fuck up.