A few things make no sense
So, David sees the Protovision ad and wants to play those games in advance. First of all, would those even be 'online-playable' (I doubt it), so why would David assume he can just start playing them via a slow modem connection instead of assuming he has to first DOWNLOAD them?
Why would he even want to play them BEFORE they are released - is he heck-bent on playing buggy alpha versions that might not be near as good as the finished product? I mean, I can understand downloading a new game as 0-day w4r3Z, but to basically call into a corporation's modem to connect him to some dev's computer that probably wouldn't have stored his UNCOMPILED sources, unfinished graphics, etc. on THAT computer anyway and then do what? It makes no sense that he'd even consider this.
Look how much work he does just to try to get the password to the 'definitely military' system. Why would he seek help from his friends if he doesn't listen to almost anything they say anyway? If it looks military, shouldn't this give David a PAUSE at least?
If he did 10% of that work just to try to get Protivion's ACTUAL NUMBER, he could call their 'probably not a modem line anyway' and then fail that way. I mean, it's ridiculous that he does all that 'wardialing' just to find Protovision's phone/modem number, when he doesn't even try the phone book, the phone number service that he calls to try to find Falken's number later, and so on.
It's ALSO ridiculous that he doesn't realize during the research into 'Professor Falken', that this might NOT actually be Protovision, and he'd better stop before he gets into militaristic trouble. How can he know so much about Falken and NOT REALIZE it's not Protovision, and that it's military stuff?
Why does WOPR act as if it's playing those war scenarios for the first time? We are told very early in the movie, that all WOPR does is play 'an endless series of War Games' - this means, it doesn't DO ANYTHING ELSE, so it should've played all these nuclear scenarios over and over again a LONG TIME AGO already. What was it doing instead? The movie tries to have its cake and eat it, too. You can't have it both ways. Either the computer has already played all the scenarios and learned 'futility', or it doesn't spend all its time playing these games. THere are not THAT MANY games it can play, so what was it doing if the FIRST TIME it 'tries to win the game' by playing the very games it was created to play, is near the end of the movie?!
Why would 'Soviets' ever DO anything, if David is playing that side, and he stopped playing? Did WOPR take its side as well? Then how is it different from its normal playing, and why can it SIMULATE a game it is playing on those big screens as if it is REAL? Who created THAT ability and why? Its task is to play games, not to make a game seem real, so why would it do that? Why would it even have access to the screens and the other computers to make it seem Soviets have launced something?
Why wouldn't WOPR know the difference between a game and reality, wouldn't that be PRETTY DARN IMPORTANT distinction to be aware of for a system that has access to nuclear missiles?
If it takes all that security, underground bunkers, guards, passwords, two men that have to turn keys at the same time to launch the missiles, why can just 'one desk clerk' in the war room open up a lid and hold his thumb on the 'launch missiles' button and basically launch the missiles? This is the room that was just VISITED by people from 'Birmingham' (if I remember correctly), so any wandering kid could accidentally have started World War 3.
This movie shows us so many nonsensical and contradictory things to its own, established rules, it boggles the mind. I mean, this ordinary-looking middle-aged moustache wielder guy is TRUSTED to start World War III and he can do it simply by opening up a plastic cover and pushing a button with his thumb, no passwords, codes, secret bunkers, etc. needed.
Also, doesn't this put the situation BACK to where it was - missiles are launchable by a HUMAN THUMB anyway after all that trouble of installing WOPR? The two men were replaced, but why can THIS ONE MAN launch the missiles? This makes NO SENSE whatsoever!
How likely is that this secluded loner that never goes anywhere and just flies R/C dinosaurs in the sky, that also has a ferry to visit the island regularly, has a gosh-darned HELICOPTER but not any kind of boats? Do people even understand how much helicopters cost, how much maintenance they require, how noisy and disruptive they are?
Also, wouldn't it be IMPOSSIBLE not to notice a gosh-darn HELICOPTER hangar/launchpad/facility that it ABSOLUTELY requires to remain in flyable condition when you visit that small island? If they can explore the island WELL ENOUGH that they can definitely declare he doesn't have a boat, HOW THE HECK DO THEY MISS A DARN HELICOPTER that takes so much more space than a boat would? It makes no sense!