God has a purpose for everything He does and though He certainly is not obligated to explain Himself to any of us, He does typically reveal His motives through Scripture.
When discussing Romans 8:29 Calvinist’s will typically argue that a personal intimacy is in view.
Do you believe every single person’s life is valuable and worthy of being protected in the womb from the time they are conceived?
If non-Calvinists are wrong, what temporal or eternal harm have we really caused?
Calvinism teaches that God foreknows because He decreed that man would act a certain way, and thus man necessarily acts a certain way and God can be certain of that.