There are several reasons for this. God tests the hearts of his people to see if they love his gospel. Satan opposes the gospel with unremitting vigour. Men love darkness instead of light, and if they will not choose to express this by atheism, or false religion, then they will choose corrupted forms of the gospel.
We may wish that it was otherwise because it grieves us to see the truth distorted and those who need the gospel being confused, deceived, or confirmed in their views that the bewildering variety of Christian claims equals an uncertainty about God's revelation.
This is the reality. It is not going to change. Handling these matters is difficult. There is the temptation to compromise, to be impatient, to be inaccurate in prosecuting error, to be loveless either to God or to those we oppose. Theological controversy calls for a heart of wisdom, grace, and conviction. Error must be opposed and truth advanced. We will never be adequate to the task, but our own inadequacies are never to be the cause of neglecting our duty.
How should we respond to it? Here are some observations from Robert Traill:
It is a sad, but true observation, that no contentions are more easily kindled, more fiercely pursued, and more hardly composed, than those of divines; sometimes from their zeal for truth; and sometimes from worse principles, that may act in them, as well as in other man. (p. 253)"Further to this good end," says Traill, we should do the following:
1. Let us not receive reports suddenly of one another. In times of contention, many false reports are raised, and rashly believed. This is both the fruit and fuel of contention.[And just think how this point is magnified by the use of broadband and blogs!]
2. Let us make Christ crucified our great study, as Christians; and the preaching of him our main work, as ministers...all things that come in Christ's room, and justle him out, either of hearts or pulpits, are like abominable to a Christian.Robert Traill, The Doctrine of Justification Vindicated from the Charge of Antinomianism, p. 281-2
3. Let us study hard, and pray much, to know the truth, and to cleave unto it. It is an old observation..."Before Pelagius even the fathers spoke more carelessly;" meaning well, and fearing no mistakes in their hearers. Now it is not so; and more careful should we be in our doctrine.
Let us search our own consciences, and see how we ourselves are justified before God...And let us bring forth that doctrine to our people, that we find in our Bibles, and have felt the power of upon our own hearts.
4. Let us run not into extremes, upon the right or left hand, through the heat of contention; but carefully kep the good old way of the Protestant doctrine, wherein so many thousands of saints and martyrs of Jesus have lived holily, and died happily, who never heard of our new schemes and notions. (p. 281-2)