"the relative security of the gay ghetto"
1.any segregated mode of living or working that results from bias or stereotyping;
"the relative security of the gay ghetto"
"no escape from the ghetto of the typing pool"

this is the defnition of the ghetto
so in this sense, it refers to the mode. a fashion , a way. right?

what does "the relative security of the gay ghetto"mean exactly?

2. is in passing same as by the way? can they be used interchangeably?

Question

"the relative security of the gay ghetto"
1.any segregated mode of living or working that results from bias or stereotyping;
"the relative security of the gay ghetto"
"no escape from the ghetto of the typing pool"

this is the defnition of the ghetto
so in this sense, it refers to the mode. a fashion , a way. right?

what does "the relative security of the gay ghetto"mean exactly?

2. is in passing same as by the way? can they be used interchangeably?

Answer

"Ghetto" is figurative in both your examples.  I worry that your understanding is a little too neutral; the word suggests a low-class, close-knit community.

Honestly, I'm trying to find the "gay ghetto" quote in another place other than a dictionary site.  Unless you can find the original quote, I'd leave that as an unanswered question.

For "in passing" vs "by the way", I don't agree that they are interchangeable. "By the way" is more like a comment in the sentence. "In passing" is part of the sentence.