Yes, purchasing life insurance is optional. If you wish to waive the life insurance, you must select this option when completing your "Designation of Beneficiary/Waiver" form during enrollment. However, please note that if you waive the life insurance, you cannot subsequently be covered during your current VISTA service, unless you undergo a physical examination at your own expense, and are accepted by the company.
See also:
How to Waive the Life Insurance Benefit