Listening exercise AI: contradictory opinions

Question

…je refuse qu'on laisse des algorithmes décider à notre place. À mon avis, il faut que l'on mette davantage en valeur l'expertise humaine avant qu'elle ne disparaisse entièrement. Et puis, je doute que les dirigeants et les PDG fassent passer l'éthique avant les profits. 
 
I realise that the euphonic "l" in "que l’on" and the ne explétif aren’t always used in spoken French. In the extract, is there a logic to adding l’ before "on mette" but not "on laisse"? And for using a ne explétif after avant que but not after douter que?

Céline Pickard · Accepted Answer

Bonjour Anne,
There is not a specific reason other than one is higher register (que l'on) than the other (qu'on / used more often in a conversation which is the case here ; this is also valid for the ne explétif). But, there's also a slight pronounciation issue: "Je refuse qu'on laisse" is easier to pronounced than "je refuse que l'on laisse" due to the 2 [l] sounds.
I hope this is helpful.
Bonne journée !

Céline Pickard · Answer

Bonjour Anne,
Yes, that's quite an astute observation! I would agree with you. Bravo ! 
Using the "ne explétif" is way more common/natural/expected even with "avant que" compared to with verbal expressions such as "douter que". This is not a nuance that is taught really. The more you you encounter these expressions, the more you'll see when the "ne explétif" is used or not and the more you'll develop a feel for it.
 
I hope this is helpful.
Bonne journée !

Anne Davies · Answer

Thank you, that’s helpful but it seemed odd to use a ne explétif with only one out of the two expressions which could trigger one. Maybe it’s used in conversation more commonly after avant que than after douter que?