In the interest of objective balance, I will stipulate that "fellowship" can be a positive community activity and if this is centered around a common belief or commitment, this may itself not necessarily be a bad thing.
However, I have attended church on occasion to expand my own knowledge and I was not impressed with the fellowship espoused by the preacher at those times.
When a preacher urges his congregation to only deal with others of like minds and avoid dealing or doing business with people of different faiths or beliefs, I tend to view that as exclusive and prejudicial. Not a worldview I can support. And if God's intentions are thus represented I tend to reject the premise altogether.