If there's a more controversial structure in Maine than Biddeford's MERC incinerator — the acronym stands for the Maine Energy Recovery Company — you'd be hard pressed to name it. For years Biddeford and Saco boosters have complained that the plant's noxious emissions and constant truck traffic have hampered their efforts to redevelop their communities. Now the incinerator's owner, Casella Waste Systems, has announced plans to sell the trash-to-energy plant (although the possibility of Casella just shutting MERC down here remains real). If the incinerator stops smoking it does raise an interesting question, notes Tux Turkel in the Maine Sunday Telegram: what would happen to the 150,000 tons of in-state trash that's currently being disposed of in Biddeford. Is this a case of careful what you wish for?