The Honest Trailersepisode about Ghostbusters has these words in the Starring section: "Egon, but not forgotten".
Small but surprisingly sweet, in the expanded universe that includes the comics and animated adaptations, it is revealed that despite wanting to get out a lot of the ghosts that get busted are relatively happy inside the containment unit. It's not the same as passing on to whatever comes after but for a lot of them who won't ever move on or who don't have the option its a nice respite from the chaos of the mortal world and they've made peace with being inside for the long haul.
It is also revealed that some ghosts actually approach the Ghostbusters to be let into the containment unit, for most of the ghosts, the place seems to be the equivalent of a four star hotel to ghosts, true, you have your bad seeds, who want out to cause chaos, but once most of them get in, they don't seem to mind.
Furthermore, at the opposite end of the super-powerful entities capable of warping reality, you have fairly benign spirits that don't want to hurt or bother anyone, and in some cases, are even willing to be helpful. Case in point, in the IDW comics, on the trail of a spectre in Puerto Rico, Egon and company ran across a ghost dog that they thought was a secondary manifestation of their quarry, but turned out to be a former guard dog for a factory, and was actually helping to protect people from the more malevolent spirit the Ghostbusters were after.
◊ outside the site used as the Ghostbusters' Firehouse. Including Twinkies.
