Others might not agree with me, but in this era, basketball games is soft. That's why players are not that banged in and out and to some extent could factor why players can still maintain their form despite playing 10-15 seasons.
As compare to the late 80's-90's and early 2000 wherein the game is pretty physical. Today you can go to the ring uncontested, as compare to those era that once you get inside, for sure there are going to be a lot of help and chances are you will get hurt with elbows poke in the face etc.
NBA was way more physical back in the 80s and 90s, with Detroit Pistons and their "Bad Boys" as best example of that. They based their team on very aggressive and defense oriented players like Isiah Tomas, Dennis Rodman and Bill Laimbeer, and managed to win back to back titles in 1989 and 1990. With today's rules, something like that is not possible anymore. They even had something called
Jordan Rules, special tactic to neutralise him as much as possible. Here is a YT video too, for those that would like to know more
https://www.youtube.com/watch?v=p2v0LOhjsJsBut i can understand the change of rules, as despite Detroit being very good, they were still hated by many for their style, and after all, goal of NBA is to make as much money as possible, so they worked towards that, and now we have Harden having something like 13 FT attempts per game, on average. I would like to see him play few games against prime Detroit team in 89/90 season
When you dunk on someone you get that crowd cheering like crazy to pump you up and that might affect you, without that, why would you even go for a flashy dunk? I think it could be worse because players may not feel the supporters outside of the arena for later on but just give up and not give their 100% since nobody is there.
While I agree that it would suck if some NBA games are played with no fans due Corona virus, and it would certainly be less enjoyable, I doubt that it would affect players that much. Here in Europe basketball fans are way louder, and make much better atmosphere (good examples are Red Star, Partizan, Aris, PAO and Olympiacos) , and it is not very unusual that some game are played without fans (mostly bans due some incidents), and team are still performing properly. Fans help without doubt up to certain extent, but in the end, it's all about players on the court. Let's hope it doesn't come to that, especially since playoff is near.