Generally brotherhoods, or families, are seen as a bad thing. Most families are made for the wrong reaons: because the people in charge of them are essentially afraid of conflict (which, as you may have guessed, is what this game is really all about). These same players usually have no idea how to run a tribe effectively, so the family usually ends up being very poorly coordinated.
When a family tribe is run well and for the right reason, though (e.g. to team up and coordinate closely against a much larger foe rather than just find safety in numbers), they can be very effective in dominating a world. This doesn't happen too often though, which is why people are usually dismissive of families which aspire to this.
