Nonsense.
How would it be any different from something like playing two different games that run at different framerate back to back...(for your "that fast part"). Campaign also plays different from multiplayer so it is pretty much like two different games. You don't play campaign over and over everyday for years...you do when when it comes to multiplayer though.
If this game was 30 FPS then by your logic you'd still complain since you could play Halo4 and all other Halo at 60FPS on Xbox One and according to your experience that would be very jarring. I'll repeat again, if Halo 5 becomes your main game you still won't be playing the campaign regularly.
Your reasoning would make sense in a game like Destiny where PvE and PvP are integrated together deeply but not in Halo where both of them will be separated far apart and you actually jump between PvP and PvE constantly and on a regular basis almost everyday.
its different from playing two different games because I'm actually playing the same game. Your logic is really bad, and you're totally misrepresenting what I said and making a lot of assumptions. I'm not saying that this game should be 30fps, it's 60fps or bust for me. Any future halo games which are not running at 60fps will be a disappointment. That really makes a lot of your post kinda pointless and just plain silly.
And it's not like SP and MP are significantly different experiences. They should be and in fact are somewhat similar. That part of your post was also a bit... wrong. Regardless of how much time I spend in single player I still want it to be consistent with the rest of the game. The difference between the way the single player would feel and the multiplayer would feel if they ran at different frame rates would be absurd and jarring. The best example I have is splatoon. The game runs at 60fps everywhere except the city hub which runs at 30. It's a part of the game you spend relatively little time in but when you do go back into the city hub it's a jarring difference moving around, even if it is just for a few seconds to go to the stores or tower. They should have done whatever possible to make that zone run at 60fps because consistency is important. Though at least in Splatoon their excuse is that there is no real gameplay in the hub. Halo wouldn't have that excuse for its campaign.
Ultimately anyone asking for the game to run at anything less than the objectively better 60fps shouldn't be listened to. And luckily for the game's sake they aren't being listened to. I feel that the people asking for stuff like this are the people who will play the campaign like once or twice, play the game for a month, and then move on to the next flavor of the month. Luckily 343 seems to be listening to the people who will likely be playing this game for a long time and intends to stick with 60fps.