This is one of my favourite topics... I'll start with saying, I don't think I'd be lying to myself if I assume I have one of the best benches in the league, and theoretically should be in favour. However, I am very much AGAINST expanding starting rosters for the following reasons:
Decreases human error: When you can just start everybody, there's no picking and choosing to be had. Part of the fun is trying to play the best strategic lineup to win your matchup, outsmart your opponent and sneak out extra points.
Decreases activity: Similar to the above, you have to pay less attention to your team because worst case scenario you leave one or two guys on the bench by accident, not five. Psychologically, your risk has gone down, and you don't care as much to check the league and set your lineup.
Decreases trade activity: All of a sudden, you're always using all of your players. The set up now means that you could be continually sitting the same player on your bench for weeks - there's no emotional attachment and you're more willing to listen to trade offers. This helps keep talent moving around the league, and provides opportunities for the lower teams to pick up some players they may otherwise not have access to. A good example of this was me continually leaving Landeskog on my bench on busy nights, and it got to a point where I was entertaining offers for him over that timespan.
Decreases parity: Lets face it, the top 4 teams have a way better bench than the bottom 4. By opening up more starting roster spots, all that does is encourage wider spreads and wider margins or victory for stronger teams. Does Biz benefit from more man games from Tyler Ennis and Jiri Hudler? Not really. But do I benefit from more games from Landeskog and Elias Lindholm - most definitely.
Overall, I think increasing starting rosters would not be helpful for the league at this point in time. Open to hearing other sides though.