Prefer在表达“我宁愿你做了/没做什么事”要用虚拟用法,这是表达与已发生的现实相反,确实和wish类似
举例来说：I prefer/wish that you hadn't killed that guy.用过去完成时
但据我所知也有“我宁愿怎样怎样”,表示一种期待的虚拟,和suggust用法一样,+或省略should
所以你问题是第二种情况,should+动词原形,should可以省略.这里usually prefer that they（should） be evaluated according to their intentions and feelings.省略了should.