Why can four-man premades kick?

[Pence]

I don't really understand the logic behind allowing this.

I just joined a fresh CT with four people who were queued together. After King Behemoth, I said 'I just got my Black Mage to rank 10 in Bravely Default.'
One of the tanks in my party, part of the group of four, said 'probably the highlight of your night, nobody cares.'
I responded 'It's a toss up between that and watching you try to pick up a giants.'

We get to Acheron and the group of four kicks me as they pull. The three other party members say 'wtf?,' 'how is he harassing you,' and 'im not kicking him.' Thus wasting an hour of my time.

This really shouldn't be possible.

Majority needs to vote. One of those people you believe were on your 'side' voted to kick you. It's initiating player + 4 votes.

[Lunasumerin]

That's not true. I was in a party of 8 and me and my 3 friends were all kicked from the group while we were in a cutscene. It was only the four other people that voted to have the first one of us kicked. So it was just the initiating person and 3 other people voting. Half of the party in essence voted us out. So its not majority. Its only 50%.

[Viridiana]

Majority needs to vote. One of those people you believe were on your 'side' voted to kick you. It's initiating player + 4 votes.

From the French patch notes:

Dans le cas d'une petite équipe, il suffit qu'un autre joueur que celui ayant demandé l'expulsion approuve pour obtenir la majorité et valider l'expulsion.
Dans le cas d'une grande équipe, il suffit que trois joueurs autres que le demandeur approuvent pour obtenir la majorité et valider l'expulsion.

Translated, that'd be:

In the case of a Light Party, one other vote is needed to count as a majority to approve an expulsion.
In the case of a Full Party, three players other than the requester suffices to count as a majority to approve an expulsion.

So, yeah, I could join a light party with 1 friend or a full party with 3 friends and kick anyone we wanted to.