Have you ever been 'the only' one in a room among 'others' who were unlike you?
The choices could be - political, religious, racial, nationality, gender --
Depending on your age and experiences, you were uncomfortable or perhaps not so much.

How do we overcome such differences and feelings of isolation in these circumstances?

Attempt to bridge whatever gap appears to exist. We do that by seeing our commonality. We are all human beings. We all have some degree of wanting to be accepted.

Being the only is no reason to become defensive, offensive, withdrawn or anxious.
It is natural to feel that. If we recognize the reason for the feeling, we can take steps to conquer it.

This is an attempt to convince myself that going to my reunion will be positive thing. That I will relax among those who are at opposite poles of my thinking, and beliefs, that I will not attempt to persuade anyone to my way of thinking--but I will share my thoughts with courage--regardless of the response.