[Question] How do most utilitarians feel about “replacement” thought experiments?

In this pa­per, Si­mon Knutsson dis­cusses an ob­jec­tion to stan­dard util­i­tar­i­anism: that it en­dorses kil­ling many (or all) ex­ist­ing peo­ple if that leads to their re­place­ment by be­ings with higher util­ity. For ex­am­ple, he lays out the fol­low­ing thought ex­per­i­ment:

Subop­ti­mal Earth: Some­one can kill all hu­mans or all sen­tient be­ings on Earth and re­place us with new sen­tient be­ings such as ge­net­i­cally mod­ified biolog­i­cal be­ings, brains in vats, or sen­tient ma­chines. The new be­ings could come into ex­is­tence on Earth or el­se­where. The fu­ture sum of well-be­ing would thereby be­come (pos­si­bly only slightly) greater. Tra­di­tional util­i­tar­i­anism im­plies that it would be right to kill and re­place ev­ery­one.

Peo­ple who iden­tify as util­i­tar­i­ans, do you bite the bul­let on such cases? And what is the dis­tri­bu­tion of opinions amongst aca­demic philoso­phers who sub­scribe to util­i­tar­i­anism?