Few if any would argue that the NFL's current schedule format isn't just right.
All division rivals play 14 out of 16 of the same opponents; every team plays four games against first-place teams from the previous season, four games against second-place teams, four games against third-place teams, and four games against fourth-place teams, regardless of where a given team itself finished.
All teams in different divisions within the same conference are assured of meeting at least once every three years, with non-conference opponents always playing each other every four years.
But sooner or later, there is going to be expansion in the NFL. Increasing the number of games from 16 to 18 will allow the league to maintain the integrity of the schedule format virtually in perpetuity.
That is to say, teams in different divisions can continue to have guaranteed meetings every three years (within the same conference) or four years (outside the conference), plus every team can be guaranteed a fair strength of schedule.
Even with as many as 40 teams (four five-team divisions in each conference) each team could play its division rivals twice each, all five teams from a division of their own conference, and all five teams from a division of the other conference, for 18 games.
Every team in the same division plays 18 out of 18 common opponents under this format.
With fewer than 18 games, either the regular-meetings principle will need to be corrupted, or the fair-strength-of-schedule principle.
Some historical background is in order:
From 1975 through 2001 (the year before the NFL adopted its current schedule format, coincident with the 2002 realignment), there were nearly three dozen situations in which two teams in different divisions of the same conference went at least seven years without playing each other (in the regular season).
In ten of them, there were at least 10 years without a meeting, and in four cases, two non-division opponents in the same conference went a whopping 13 years without playing each other!
This was because, from 1978 onwards, the league made an admittedly imperfect effort to smooth out differences in strength of schedule by trying to make "good" teams play each other and "bad" teams play each other.
But what if two particular teams were never "good" or "bad" at the same time?
Prior to 1978, it was even worse: There was sort of a rotation system in place that had most teams playing each other every few years; but nearly a decade's worth of non-division matchups were predetermined when the NFL and AFL merged in 1970, without any regard to how strong or weak each team might be down the road.
This often led to massive imbalances in strength of schedule.
In 1976, for instance, the Giants (who had been 5-9 and fourth in the then five-team NFC East in 1975) had to play, in addition to their eight division games plus one game against the expansion Seattle Seahawks (who played every other team in the NFC that year), three teams that had won their divisions in 1975, and two that had finished second.
Predictably, the '76 Giants fell flat on their faces, finishing 3-11, and firing their head coach, Bill Arnsparger, seven games into the season (the Giants were 0-7 at the time, and had been heavy underdogs in every game but one).
A return to either of these scenarios is clearly and totally unacceptable. Eighteen games would prevent a recurrence of either for decades to come.