Look at it from another perspective: Voldemort’s actions are based on the belief that Harry has powerful secrets unknown to him. One or more of those secrets may well lead to the end of the world if Harry lives. Given that Voldemort is acknowledging his ignorance of Harry’s full capabilities, is there any possible excuse for not trying to limit those capabilities as much as possible?
Look at it from another perspective: Voldemort’s actions are based on the belief that Harry has powerful secrets unknown to him. One or more of those secrets may well lead to the end of the world if Harry lives. Given that Voldemort is acknowledging his ignorance of Harry’s full capabilities, is there any possible excuse for not trying to limit those capabilities as much as possible?