Many people would answer that this is a homophobic invention. Gays live there lives in many different ways, as straight folks do.
So is it completely non-appropriate to talk of a "gay lifestyle"?
Let's take a closer look at what Wikipedia has to say:
"Lifestyle is the interests, opinions, behaviours, and behavioural orientations of an individual, group, or culture. The term was introduced by Austrian psychologist Alfred Adler with the meaning of "a person's basic character as established early in childhood", for example in his 1929 book "The Case of Miss R.". The broader sense of lifestyle as a "way or style of living" has been documented since 1961. Lifestyle is a combination of determining intangible or tangible factors. Tangible factors relate specifically to demographic variables, i.e. an individual's demographic profile, whereas intangible factors concern the psychological aspects of an individual such as personal values, preferences, and outlooks.
A rural environment has different lifestyles compared to an urban metropolis. Location is important even within an urban scope. The nature of the neighborhood in which a person resides affects the set of lifestyles available to that person due to differences between various neighborhoods' degrees of affluence and proximity to natural and cultural environments. (...)
A lifestyle typically reflects an individual's attitudes, way of life, values, or world view. Therefore, a lifestyle is a means of forging a sense of self and to create cultural symbols that resonate with personal identity. Not all aspects of a lifestyle are voluntary. Surrounding social and technical systems can constrain the lifestyle choices available to the individual and the symbols she/he is able to project to others and the self.
The lines between personal identity and the everyday doings that signal a particular lifestyle become blurred in modern society. For example, "green lifestyle" means holding beliefs and engaging in activities that consume fewer resources and produce less harmful waste (i.e. a smaller ecological footprint), and deriving a sense of self from holding these beliefs and engaging in these activities. Some commentators argue that, in modernity, the cornerstone of lifestyle construction is consumption behavior, which offers the possibility to create and further individualize the self with different products or services that signal different ways of life.
Lifestyle may include views on politics, religion, health, intimacy, and more. All of these aspects play a role in shaping someone's lifestyle. In the magazine th, and television industries, "lifestyle" is used to describe a category of publications or programs." (https://en.wikipedia.org/wiki/Lifestyle_(sociology) September 7th 2019)
Are there common interests, opinions, behaviors, and behavioral orientations in the gay scene? Anyone who has ever been there would definitely agree. There is a special way of talking, of celebrating, a different way of dressing up, different interests and values than compared to the rest of the population (yes, there will always be some who drop out of this classification, but on the average this might be a true statement). I have been there for many years and from my experiences I can definitely agree.
My "lifestyle" and that of many others I encountered reflected our attitudes, our way of lives and world views - no doubt about that. The environment we were living in also constrained our lifestyle choices. I could absolutely agree on that one as well. And yes, my views on politics, religion, health and intimacy were shaped by it as well and formed what you might call a "lifestyle" that I shared with many others then.
So all in all there is a "gay lifestyle".
The question is rather why so many gays are annoyed by this term? I guess they want to present an image to the public that makes them look like an ordinary John Doe, just like everyone else. But they are not! Gay activists use that as a propaganda technique - being well aware that the reality is way different. If I'd still be in the gay life, I would be more than happy to embrace a "gay lifestyle" - probably even be proud of it. Could it be that the gay self-confidence and self-assurance is so low it needs to look like everyone else and is ticked off by being called "gay"?
Recently, I communicated with gay men in online dating sites (not that I recommend that!). My impression? The more things change, the more they stay the same. Nothing much seems to have change since I left 15 years ago. Just take a look at the CSD-parades each year and tell me there is no "gay lifestyle"! To claim there is not is ridiculous and every gay person knows it.
I am ever so glad I left the environment that shaped my life back then. The way I live my life now does not fit any category and I am more than happy about that.