Starting them is selfish, joining them, while not selfish, isn't selfless because if ONE person is doing it, 2 of the others (including you until you saw it) had every intention of playing the game.
While I understand 100% this is a game, it's still a team effort, all sports are, so I prefer to put these scenarios in to real world situations as comparison. What about the games played in sports during pre-season? They don't actually matter, they are just practice and for fun, so it's okay to drop down on the pitchers mound and flop around in hopes the rest of the team will too? Everyone will kick you off the team and ask you to leave. "But, it's just practice, it doesn't matter because the season hasn't started yet"...yeah, that's gonna fly. Is it fun to load up say Super Mario 3D World and run around in a circle jumping up and down? I'm going to guess no. Do you see this being done in ANY other online shooter game in existence? No. It literally makes no sense to do it.
First of all, concerning it being done in any other online shooting game in existence? I'm pretty sure it happens in
Team Fortress 2.
It also has a history of being done on Nintendo online. (See
Super Smash Bros. Brawl and
Super Smash Bros. 4's For Fun mode.)
Okay, here's what the semantic game designer in me would say:
You keep using “playing” as the verb, right? So, squid partying is
exactly that. It's playing.
It's playing with the system the game developers have created. You talk about intent of the game designer, and I say this — the designers had
every intention to make the controls of
Splatoon feel great. It was entirely purposeful to have just the very movement of your Inkling feel awesome.
How can you then fault players for enjoying that, and wanting to enjoy that with their friends? There is a very valid motivation for playing
Splatoon that I personally have: That is the social, community aspect of it. This can be shared with competitive motivation, or it may be one or the other.
Nintendo's developers want their games to appeal to a wide demographic of people with a wide variety of motivations for playing. That's why they have Ranked and Turf Wars as different lobbies. That's why there is For Fun and For Glory. It's why you can also search in the Wii U's friend list people you've played online and find them and send them friend requests, or go to their Miiverse and talk with them. And I've done this after squid-partying with people. They attach to me like flies and honey when they see a friendly, sympathetic squid flopping around with them. They go through enemy lines just to be reunited with me! It's touching. And impactful. Much more memorable to me than the competitive parts.
You can treat squid partying in unfriendly territory to be like a game-within-a-game, or a game that is an added layer put on top of the base
Splatoon. That only enriches the experience. It doesn't detract it.
And if 3D World has those kinds of movement options that are fun, then yes, that's fun. Personally, I enjoy the dashing options in the
Mega Man Zero games, so I dash around aimlessly in-between levels.
Got a problem with that? Blame the designers for making it so smooth.