That's a pretty unfair characterization of the overwhelming majority of scientists. It is always possible to find individuals at the fringes of any field who advocate things that fall outside the mainstream. Unfortunately those folks are often the people who shout the loudest and get quoted by the press. Science works by building consensus, so when people say the scientists don't agree...that is a normal thing and just the way it works. However, agreement (mostly) comes about after a time via groups repeatedly finding the same results and through different ways of approaching answering the question and arriving at the same result. Science is also a bit weird in that it doesn't ever really PROVE anything....instead the approach is generally to reject all the alternative answers.
To return to the topic at hand, I think MOST scientists who actually WORK in the maple field recognize that there have been changes in the timing of the maple season and are concerned about the long-term viability of COMMERCIAL maple production in some areas, particularly those in the southern edges of the sugar maple range (where periodic high temps during the season just kill sap flow), but by and large they tend not to be the doom and gloom types who suggest that maple production will end soon. Lumping all of these folks (self-included) with those who either don't really know about maple, those with some agenda, or are just happen to be out on the fringes is a real disservice.