1. We're all poor and powerless - When Muslims line up for prayer, no one is able to distinguish between Sunni and Shia based on their dress or knowledge. All of the masses of people have taken our religious information from leaders and scholars who may or may not have been correct.
Islamic history is rich with both violent fracturing and civilized disagreement. However Muslims must not allow political or religious leaders to dictate how we treat one another in everyday practical situations after we have such a rich history of mistakes to learn from. As a Sunni majority in America, we're in a country that has accepted those of us who've come here from other places, should we then discriminate against others? If so, we'll be doing the exact same thing to Shia Muslims, that we complain Americans do to mainstream Sunnis; marginalizing them and not giving them a chance to "Be."
2. We worship one and the same God - All three Abrahamic faiths, Judaism, Christianity and Islam, worship the same one true Lord although we each use different Names for Him according to our languages. However you would think from the behavior of some Sunnis toward Shia that the Shia pray to a carton of eggs or a box of cereal. They don't. They pray to the one true God.
The prophet Muhammad said:
Whoever sincerely says that 'None deserves to be worshipped except God' will enter paradise. (Sahih Al Jaami)
He said that if this testimony of faith was put on a scale and all of creation was placed on the other side, the testimony of faith would weigh heavier on the scale than everything in existence. If that's the case, then the details will be sorted out by God and everything after this testimony is up for debate.
3. We follow Muhammad - As Muslims, both Sunni and Shia, we take prophet Muhammad as the final inheritor of God's message to all of mankind. God says:
Muhammad is not the father of any one of you but he is the Messenger of God and last of the prophets. And Allah knows all things. (Quran 33:40)
After this statement in the Quran, the hadith narrations which have been collected as the sayings of the prophet, are a controversial lot. Of course Sunnis think our sources are better and of course Shias think our sources are tainted. So what. Hadith did not drop down from the sky through revelation like Quran, they are simply words passed down from man to man. Mistakes are bound to be mixed within them. It's not worth our unity to fight over them.
4. No one else knows the difference - When a hate crime is committed against a Muslim, perpetrators don't stop and ask, "Wait, are you Sunni or Shia? Because we only burn down Shia Mosques."
5. The companions disagreed among themselves - When the prophet Muhammad went to the heavens during the trip known as Mi'raaj, Abu Dharr, his trusted companion later said after Muhammad's death:
The prophet saw his Lord on the Mi'raaj. (Sahih Muslim)
Aisha, the widow of Muhammad heard about this and remarked:
Whoever says the prophet saw his lord has invented a lie against God. (Ahmed's Musnad)
This was a serious issue. Likewise, the very founding of the four schools of jurisprudence within Islam, is based on a fundamental disagreement that says I believe I'm right with the possibility that I'm wrong and I believe you're wrong with the possibility that you're right.
6. Abu Bakr and Ali were just men - During the Treaty of Hudaybiyah when Suhail ibn Amr who was not Muslim, refused to refer to Muhammad as the messenger of God during the writing of his name for the contract, the prophet didn't mind. He didn't make a big deal about this although he was certainly the messenger of God. Therefore whether Abu Bakr or Ali should have been the head of state after his death is a political difference that shouldn't interfere with our contemporary condition in such a way that it stifles any constructive progress not just for individuals but for an entire region of the earth!
In conclusion, opinions and discrimination are luxuries for those who have comfort. However if you found yourself powerless, naked, covered in dirt, hungry, wet and cold and a human being came to your aid with a crumb of bread, or a bowl of soup, or a cup of water, or a dry shirt, the last thing you would ask them about before you partook in their charity is their religious affiliation.
Let's be human together, before we call ourselves anything else and while we still have the chance.