Both L and Kira were right.
-Kira was right in saying there is no justice because millions of people with money or just privilieges go unpunished all the time from their crimes.
-Kira saw an opportunity come by and together with a very nice god complex he took action since no one else was. Kira was taught by his father to take action because he was in the police force too so thats part of hus reasoning.
-Apart from that, what Kira meant about the "god of the new world" was in a literal sense. Many religions right now rule with fear, fear of going to hell or other punishments which makes people repent their actions and try to find good.
-Kira also ruled with fear, with the threat of "if you do something punishable by the law, you die" so everyone started slowly understanding and supporting him just like we do religion.
( i dont mean to insult any religion at all please believe what you want its fully youf choice sorry if i offended you.)
-L was right because he was trying to stop Kira from killing people, innocent or not. If it had been a diffrent punishment however L would not have taken action because killing wouldnt be involved.
-L was also wrong at the same time for trying to stop Kira who was essentially doing the right thing with the wrong punishment.
-The scene where Kira and L get down from a wet rooftop and Kira rubs L's feet was a strong reference to the bible where God rubs and cleans Judas' Feet, even knowing he was the traitor.
-Thats why Kira (the god of the new world) was rubbing L's feet, considering him a traitor because he was stopping the "justice" Kira was implementing by threatening people with death if they commited any sort of crime.
sorry to disappoint but im team Kira for sure