There are two main reasons why teachers should alleviate these concerns. They are going to have to have children with special needs in their classrooms, so they might as well get over their worries.
First, getting over their worries will help them. The more that a teacher is worried about the prospect of having special needs students, the more difficult teaching will be for them. They will be constantly worrying about how the special needs students will do in their room. This will distract them from their teaching and it will make their job less fulfilling.
Second, getting over their worries will help their students (both the special needs students and the others). When the teachers are less worried, they will do a better job of teaching. That will help all of their students. When they are less worried about the special needs students, they will do a better job of interacting with those students. They will not project an attitude of being worried about those students and will not make the students feel like the teachers wish they were not there.
In these ways, it is important for teachers to alleviate their concerns about special needs students.