In fact, the opposite is true.
Keeping slots illegal in Massachusetts prevents the establishment of tribal casinos.
But legalizing slots makes tribal casino more likely.
When the Mashpee Wampanoag Tribe received federal recognition in February 2007, many people beleived that Class III gambling (slots machines) would be inevitable in Massachusetts. This bit of misinformation was used to convince many Middleboro voters to believe that a casino was inevitable.
Tribes cannot engage in any form of gambling on their sovereign territory that is not legal in the state. The state cannot be compelled to sign a compact for gambling with a tribe.
What about the "Vegas Night" exception? Can having legal one-night charity games open the door to tribal 'gaming'? No. Texas, like Massachusetts, has a lottery and Vegas Nights (one night licenses to operate slot machines for charity) but slots are illegal. Tribes there tried to prove that this created precedent for allowing tribal there casinos to offer slots. But courts disagreed that this wasn't a compelling argument since Texas has shown a consistent history of opposing level III gambling. Like Massachusetts.
Tribal gambling enterprises must be established on tribal lands - sovereign territory - property that has been removed from state tax rolls and taken in trust for the tribe by the federal government. There is a separate, even more complex process required for taking land in trust for 'gaming'. In some cases, the host community must approve the application. In any event, tribes must submit a detailed application to the government to put any land into trust, and it is not always a sure thing. In recent years regulations regarding the taking of land into trust, especially for 'gaming' have become more restrictive.
Matters were further complicated for the two federally recognized Massachusetts tribes, the Mashpee and the Aquinnah Wampanoag when, in February 2009, the the Supreme Court of the United States ruled in the case of Carcieri v. Kempthorne (now known as Carcieri v. Salazaar) that the Indian Regulatory Act did not apply to tribes recognized after 1934. Consequently, the Indian Gaming Act would also no longer apply to tribes recognized after 1934. Both of these Massachusetts tribes were federally recognized well after 1934.
Shortly after the Salazar decision, in Hawaii v. Office of Hawaiian Affairs, the Supreme Court ruled that,
"Congress cannot, after statehood reserve or convey submerged lands that have already been bestowed upon a State" - further reducing the likelihood of any Federal land-in-trust acquisitions in Massachusetts.
In her testimony before the legislative Committee on Economic Development and Emerging Technologies in June 2009, Massachusetts Attorney General Martha Coakley stated that
"The Supreme Court's decision this past February in the Carcieri case effectively puts the Wampanoags and other tribes in Massachusetts on the same footing as any other private party because the Secretary of the Interior's ability to acquire land for Native Americans is limited to those already under Federal Jurisdiction at the time the Indian Reorganization Act was enacted in 1934. Massachusetts' Native American tribes each came under Federal Jurisdiction after 1934. As a result, they are entitled to make an application and bid for a gaming license like anyone else, but do not have special entitlement to conduct gaming under the federal Indian Gaming Regulatory Act or the Indian Reorganization Act."
However, if a state does legalize class III gambling, either through casinos, racinos or slot parlors, Tribes can ask Congress to give them land into trust for 'gaming', claiming the state has an unfair economic advantage, and they would have a good case.
For example, Florida had consistently managed to keep the Seminole tribe from winning their bid to bring slots to the state. The Tribe was allowed to offer level II gambling (the much less lucrative bingo slots which managed to attract gamblers mainly because there was no other slot-style 'gaming' for 600 miles around.) But
Vegas-style slots are where the big money is. The courts, however, consistently backed Florida by ruling that the State did not have to sign a compact for expanded gambling with the Tribe. But then the State granted a slot licence to a racetrack, and the tribes were allowed to open full-fledged mega casinos.
It should be noted that there are currently 2 recognized Indian Tribes in Massachusetts, and 6 other Tribes which could seek recognition. Approving slots at the racetracks could open the door to 8 Massachusetts casinos.