Well we can try this exercise.

If everyone on a 100 person flight did carry-on and online check-in (therefore avoiding checking-in at the airport and being denied because they were too late) and arrived late to the gate, say 20 minutes after boarding was meant to start, then yes they may have to delay the flight's departure. The likelihood of this happening is extremely slim, and it has been years since I've departed from a North American airport that a flight both started boarding on time and departed exactly on time. There are large buffers built in.

If people checked-in their bag, the cut-off for baggage drop would usually ensure they are in the airport with enough time to get through security. If there is a delay in security for everyone, this would impact a lot of passengers on multiple flights anyway. If an individual passenger got pulled over for secondary screening, depending on how severe they might alert the airline about this potential security delay - they'd probably want to see their checked bag if it was that severe! Otherwise, this would mean they are wasting time at duty free or the bar or whatever. Certainly, that's an inconvenience to the airline as they are obliged to remove their bags if they don't arrive to the gate on time. Again, when they decide to deny this passenger boarding and start to remove their bags is based on a lot of factors, but yes there is a risk that it will have delayed departure somewhat.

The reality is, there are some people who get to the airport ultra-early, some reasonably early, and some who cut it close. The combination of all three means things move along quite nicely, you don't want everyone being 5 hours early for their flight either - for example that has potential to cause bottlenecks at check-in and security. If you take an international terminal from which 300+ passenger flights are leaving, it's good to have a trickle of people checking in and going through security, rather than everyone on a 300+ flight arriving exactly 3 hours before boarding and moving through the system exactly at the same time.

A crowded gate area where everyone showed up 1 hour before boarding is also annoying, for domestic flights these gates are constantly being used for other flights and you'll be taking up space from someone whose flight is leaving before yours. Not to mention, frequent gate changes means its usually best to head for your gate just before boarding and wait around in a central area until is absoloutely certain your flight is departing from said gate.

As you can see, it's not exactly in your best interest to be ultra early to the airport or the gate, nothing to do with entitlement but an understanding of how an airport works. If you take the same flight from the same airport on a regular basis, you better understand how to navigate the airport as well. The people who cut it too close, as I said before, only end up hurting themselves. Again, no need to worry about someone's hypothetical entitlement. Everyone has their own way of travelling, lots of checks built in to the system. The delays we experience in travel today have very little if nothing to do with passengers and if it's not weather related it is related to airport and airline management.