My 300 hasn't stalled in the last 3,500 of over 4,000 miles since new. Maybe it is because of awareness / rider technique, but I won't be getting mine fiddled with for a reason I consider minor. Not trying to be a-know-it-all or wise-guy here, but I have had it with buying new vehicles and within a few months the selling/servicing dealer is trying to convince "the masses" that a fix is in order. BMW severely altered my 2003 Cooper "S" mileage and power with an "EPA" mandate within the first year - separate issue; back to Ninja 300.
If you look at the stalling thread there were a ton of theories being tossed around related to climate, average temp in the area, rain...No one could come up with a common link on exactly what caused the stalling problem to effect some people and not others.
Essentially what this means is that in your current location, at this years temperature/humidity average, with the type of gas you use....your motorcycle is not effected by the stalling problem. Congratulations! But if one of those variables change in the time you own the bike...a new gas type, a change of location, the time of day you ride...you may start stalling.
You are entitled to not have the service done, but having had a couple close calls in traffic where my engine's cut out while pulling in the clutch to shift I wouldn't want to risk getting caught like that unexpectedly. (For example trying to pass another vehicle on the highway, so you downshift for a little more power only to have your bike cut out on you in the passing lane while another vehicle is coming up behind you at 70mph).
The dealer/service department isn't really trying to convince you of anything. The OWNERS of the bikes reported a stalling issue to the NTHSA as well as Kawasaki and they found something wrong so they are offering to fix it for FREE. The Ninja 300 may be similar to a Ninja 250 but the Fuel Injection, slipper clutch, and ABS are all new...so it's not that unusual for problems to be found once the product is in actual use which is the cause for these recalls.