When it comes to objectives, it seems like whenever frigates get there, they get chased away by bigger ships (because if they do not run, they die).
If I want to capture objectives, I probably want a fast big ship, like Falcon. Currently, I use Falcons or (sometimes) Doom for the frigate role in endgame fights.
Unless capturing objectives gives a permanent bonus, making them a one-and-done deal, it seems like a better idea to send ships that can hold the points after they get there, not little ships that get there first but cannot hold the point after bigger enemies arrive shortly after, sometimes before the point is captured.
Jokes aside I feel generally the issue isn't people wanting 30 frigates, basically that'd be dumb, but rather would like a nice mix of not all cruisers/capitals without feeling like they are crippling their fleet strength. Because right now that's a cargo/fuel/salvage/ox being thrown away if not a cruiser/capital.
It was not dumb in releases before 0.7a, when fights were shorter and AI was less cowardly. Player needed some longer-range weapons and possibly homing missiles (because they passthrough friendly ships) to let as many ships as possible to focus-fire on a single enemy ship. 0.65a was really the golden age for frigates, because they could do everything except haul food (when food runs gave about four times more xp than combat). During that release, thirty-something frigates (led by Hyperion flagship) could wrap up an endgame fight in about three to five minutes, just enough time to win without too much CR decay if they had Hardened Subsystems.