This is an opt-in feature that will provide a basic, and welcome, level of spam filtering that will suit the needs of most users.
Such a feature is already available for Messages, and in essence, little different than the spam filtering applied to email, except that instead of a separate list, or spam folder, the voicemail box serves as the holding cell.
Of course, no AI is perfect, and that does result in some false positives, but for the most part, modern email spam filters are very effective. Ad blockers can break some sites, but those who opt to use them obviously feel that they bring more benefit than harm.
Phone calls are in desperate need of similar measures, and they will improve over time as well.
Those with use cases where it could be troublesome, or desire a greater level of granularity are free to leave it disabled, or seek third-party solutions that better satisfy those needs.
Unfortunately, standing still is fast becoming an untenable option so Apple deserves credit for bringing forth a feature that many of its users will find beneficial.