I think there is a certain balance that is required. No need to go all-out but some basics are essential to "fit in".
I take an example from live-action medieval re-enactement/roleplaying (which I was heavily in before airsoft).
We had people of many types :
1. Full chainmail and real leather garb with expensive latex weapons.
2. Some wore more basic clothing and some look-alike or fake armor with simple duct-tapped weapons.
3. Others would come in the game with little more then a pair of jeans, a t-shirt and a sword.
The first 2 types are perfectly fine. The third type just destroys the mood of the game and is usually not very serious in it's type of play.
Not everyone wants a full set of advanced gear and but some basics are essential to make sure you fit in the game and do not affect the overall mood. Airsoft is a game. Gear is not essential to have fun but airsoft is also a game with a mood/style and it's important to at least not look out of place.