Breeding incompetence
Downvotes incoming
In an ideal world players start their climb on ladder straight at level 1. New or not you still have a rating. The point of ratings are to tell you where you stand and they still exist in normal draft or ranked draft. It's just that there is no visible rank in normals.
To put it simply everyone who supports keeping normal draft alive are players who don't take league matches seriously, or sucks so much that they are insecure about getting a rating that accurately shows their skill level.
There is no reason to NOT play ranked. Practice? The best practice would be against other players who are playing to win, not other players who just want to practice too. Being scared of losing rating in ranked is a pitiful reason for keeping normal draft. More so if the fear is from knowingly having radical picks in champ select.
edit: Answer to all future posts: It's more likely for someone on your team to have mastery 7 on a champion and feed their butts off even when trying their hardest than getting someone on your team who simply plays to lose by picking radically incompetent champion choices in the wrong roles,(such as soraka jungle or twitch support). then again, I haven't experienced bronze or silver for a couple years. SO, hypotethical incompetent picks are not exactly a strong contention point for drafts being merged, because these kind of troll picks happen in ranked regardless of there being an open normal draft queue 24/7.