With stark pictures and dire warnings, the federal government's anti-ecstasy campaign strikes exactly its intended tone: scientific fright. In schools around the country, counselors are showing students sleek and sharply contrasting images of the brains of habitual ecstasy users and nonusers. The brain scans of nonusers show plenty of colorful activity. The users' scans are full of ominous black blotches resembling holes. "We tell them, 'Ecstasy eats your brain like a moth eats an old sweater,' " said Susan Billy, who directs the Chester County student-assistance program, a group of teachers who coach public school students on the dangers of...