Qu'ran condemns Sects

“As for those who divide their religion and break up into shias (sects), you have no part in them in the least: their affair is with Allah: He will in the end tell them the truth of all that they did.” (Quran, 6:159)

“…and be not amongst those who join gods with Allah, those who split up their Religion, and become shias (sects) - each party rejoicing in that which is with itself.” (Quran, 30:31-32)

“Truly Pharaoh elated himself in the land and broke up its people into shias (sects) … for he was indeed a maker of mischief.” (Quran, 28:4)

We learn from the Quran (the verses cited above) that dividing religion into sects is akin to joining partners with Allah, an unforgivable sin. The reason that creating a religious sect is considered associating partners with Allah is because it is playing the role of Allah since Allah alone has the right to create a Deen (faith). These people who create sects are trying to take over this role of Allah and put themselves on par with Him.
It does not matter what a person calls his or her sect–it is not authorized by Allah. Allah condemns all sects, and those who break away from the main group. This is exactly what the Shia have done. They have broken into many small sects; in fact, there are dozens upon dozens of various branches of Shi’ism, all of which follow a different line of Imams.
Allah Almighty says in the Quran: “This Day I have perfected your Deen for you and chosen Al-Islam to be your Deen.” (Quran, Surah Maidah) Nothing can be added or subtracted to Islam after this proclamation, and yet this is exactly what these various sects have done. Allah says in the Quran:

“And hold fast, all of you together, by the Rope of Allah and be not divided amongst yourselves.” (Quran)