When a group gets a large enough population, you are bound to have bad apples. Christianity, being the most popular religion, is no exception.
100% true.
Ignore Christianity writ large for a moment, and imagine various Christian communities or church groups you've been exposed to.
They absolutely vary in terms of their attitudes to outsiders. Some are welcoming of outsiders, some are basically xenophobic. Their particular group dynamics and religious beliefs can be impactful on this, both for better or worse, beyond individual variance.
For some of us, we've been exposed to Christians whose religious belief drives common respect, but perhaps more whose belief drives a feeling of superiority and exceptionalism.
I think that's what we are commonly saying, in a more detailed sense.
Incidentally most of my family and my best friends are Christian, and good people.