"it affects all competitors equally" - I think this is likely not true for most races. Boats that couldn't fetch a mark may now be on layline and vice versa.

from another thread

World Sailing Guidelines
15. Adjusting The Course To A New Wind Speed Or Direction 
15.1 Change in wind direction: 
(a) With a persistent wind shift of 10° or less the course will not be changed unless necessary to adjust for current or to provide a square run. 
(b) Between 10° and 15° consideration will be given to adjusting the course to the new wind provided that the race management team is confident that the shift is likely to persist. 
(c) With a persistent wind shift of more than 15°, the race management team will attempt to change the course to the new wind.  
(d) With a persistent wind shift of more than 45°, the race management team will consider its influence on the race.  Under these circumstances, the race management team may either change the course or abandon the race. 
(e) Frequent and violent oscillations: Under these circumstances the race management team may not be able to adjust the course sufficiently or quickly enough to maintain a race of the required standard. In this case the race may be abandoned. 
(f) Changes in current or a difference in the angle of the current relative to the wind may justify variations from these guidelines. 

I think ideally the RC would have liaised with the competitors' representatives (eg CA for a Championship) and agreed an understanding of how the sailors would like major shifts, calms and so on handled. Some fleets are quite happy with endless resets and abandonment in difficult weather, others just want to go sailing and prefer to put up with the dice tosses. If a race has turned into a procession some may prefer it to be aggressively shortened rather than abandoned. 

Tiziano .. there are a couple ways to look at your question.

First the rules question you asked .. 

The RC " may" .. so unless other documents state otherwise (Race Doc's, CR, Championship/Race Conditions), it is the opinion of the RC as to what is "fair".  When a committee "may" do something, it's completely their option to do something or not.  Neither decision (abandon/not-abandon) is an improper action or omission by the RC eligible for challenge in a redress hearing.

Beyond that, you can see if there are any "Conditions" set for the regatta.

Conditions for racing can be directed, with differing degree of "force", on what is necessary for the regatta.  Sometimes these have wind-shift limits within them and the actions suggested/required.  Conditions can be built into the NOR/SI for regattas of importance, the Class Rules or for Championships at different levels.

Yes the race can be abandoned, especially earlyin a race when thereis no established leader.

You do not have to abandon though. 

Here is part if the ILCA race management guidelines it says may not shall. 
13. Abandonment 

13.1 On the first half of the first leg, the race committee may abandon a race in the event of persistent wind shift of more than 25 degrees. After that, the race committee will let the race continue if it is able to adjust to the changed conditions.

https://ilcasailing.org/rules-and-technical/race-management-policies/
Separate document. Someone asked for redress because of big shifts and did not follow guidelines. Lo and behold they are not used for redress 

Agree. It is a nice document to give guidance to the OA as to how the class wants to play the game. Not sure how many know it exists