Well, duh. While the issue of NE's intentional manipulation of air pressure was the catalyst for the investigation:
Tom Brady banned 4 games for role in 'Deflate-gate;' Patriots fined, lose picks - National NFL | Examiner.com
You cannot
not investigate teams with a history of circumventing the rules in order to affect the on-field product when it becomes known that they are, once again, allegedly circumventing such rules. If you do, the inevitable cheating rumors affect the final product and, ultimately, the profitability of that product. NE put itself in the position of being subjected to an investigation b/c it has a history of seeking to manipulate the rules through off-the-field actions for an on-field advantage.
Similarly, once subject to investigation, anything other than full compliance should be harshly penalized as, once again, if the investigation looks half-assed, the cheating rumors will continue to circulate.
Sure, 1.2 psi, in and of itself, is unlikely to affect the competitive balance of any particular game. The sanction is simply not about the psi. Rather, the sanction
and investigation are directly related to preventing further spread of the perception that (1) a team is consistently manipulating the rules with its off-the-field actions to affect the on-field product; AND (2) it will actively attempt to cover-up such actions. If those perceptions are allowed to spread, it will ultimately affect the integrity and profitability of the final product
for all teams. Thus, both the investigation and sanction were reasonable under the circumstances that NE created for itself.
NE and Brady brought this on themselves. In the end, the sanctions send a clear statement that teams should not, through off the field actions, attempt to affect the play on the field and, once you have been determined to have done so once, you will be subject to an even higher level of scrutiny. Further, if the NFL investigates you, even for a minor violation, you better be forthcoming with everything.
Plus, Brady is a rat-ass liar.