An airlock can be useful though. Here's some good info on using an airlock as a diagnostic tool.
https://www.homebrewtalk.com/f13/trust-your-airlock-134640/
The thing is, the idea of "trust your airlock" rests on a big assumption (acknowledged by the OP): your fermenter doesn't leak at all.
For those of us who use plastic fermenters--e.g. the ale pale--it seems pretty common to have some minor leakage. I get very little airlock activity with most batches, because my lids must not seal perfectly. Thanks to the CO2 layer produced during fermentation, infections shouldn't be a problem (and haven't been for me to date, after a few dozen batches).
It's a cliche, but to the original poster here, I say, RDWHAHB. Every batch I've brewed has hit an acceptable final gravity, even though some never had much airlock activity at all. Three weeks in the primary does the trick for almost any normal-gravity beer under reasonable circumstances. Just check that FG and 99% of the time it'll be right where it should be.
Also, a tip: if you're using an opaque bucket like an ale pale, hold a flashlight up to the lid while the lights in the room are off. You'll likely see a little krausen ring in there, showing you that the yeast are working. I just brewed last night and noticed the airlock wasn't showing activity today, so I used this trick and noticed a krausen ring. I have since relaxed and enjoyed a few homebrews!
Edit: Apologies in advance of some of this comes up in the other thread, but I'm just trying to make a point to our OP based on my own experience. Airlocks are not a good diagnostic tool in most real-world circumstances, at least for me!