The disagreement between Luther and Zwingli over the Eucharist is a case in point. The Church has always tried to resolve difference in synods and councils. Protestants also tried to do this for disputes among them; hence the several written Confessions, and even the negotiations with Catholics trying to arrange for a Council resolve differences. The multiplicity of sects comes because people choose to follow different leaders, or because some people prefer different styles of service, but very often because two brothers read the same text differently.
8 For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, 9 not a result of works, so that no one may boast. 10 For we are his workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them.
The eucharist. OK. Some people believe that it is transformed into the literal body and blood of Christ and we're to eat it literally and physically, but that contradicts the clear teaching of much other Scripture about the eating of blood.
Looking at it as a symbolic representation of Christ's suffering and death, is a more plausible and valid interpretation. It fits with the clear teaching of other Scripture. There is no contradiction and no rationalization required to excuse Jesus doing something that violated the Law He said He came to fulfill.
That said, if someone is trusting Jesus along for salvation, then that person is saved whether or not they think the bread and wine are transformed or not.
They can be wrong about that theology and still be saved, which is something Catholicism does no grant to someone who disagrees with them.
The only ones making it a salvific issue are the Catholics. Now granted, some Protestants will probably take that stand as well, but that puts them on equal standing as Catholics in that they consider it a salvific issue, while others don't, but Catholics who consider it a salvific issue are in NO position to criticize others for taking the same kind of stand they take themselves only from a different perspective.
While Catholics are gung ho about pointing out all the differences in theology that exist and *divide* non-Catholics, what they totally fail to see is the unity of belief in the gospel of grace.
There is a lot more room for differences in theology in Protestantism than Catholicism allows for. Catholicism demands adherence to its doctrine under the threat of eternal damnation.
Protestants recognize that people are in different stages of their walk with Christ and spiritual maturity and that God will deal with what needs to be corrected in His due time. A person may have theology that is off some, but may have issues of the heart that need more attention first.
Being in right relationship with other believers and family members is more important than having all their theological ducks lined up in a row.
Head knowledge is fine to an extent. The heart is what God is after.