From Wikipedia:

The focus of the investigation centered on the foam strike from the very beginning. Incidents of debris strikes from ice and foam causing damage during take-off were already well known, and had actually damaged orbiters, most noticeably during STS-45, STS-27, and STS-87 [9]. Tile damage had also been traced to ablative insulating material from the solid rocket motors in the past. The composition of the foam insulation had been changed in 1997 to exclude the use of freon, a chemical that causes ozone depletion; while NASA was exempted from legislation phasing out CFCs, the agency chose to change the foam nonetheless. This led to many statements linking the foam strike to environmental pressures. STS-107 used an older "lightweight tank" where the foam was sprayed on to the larger cylindrical surfaces using the newer no freon foam. However the bipods were manufactured from BX-250 foam which was excluded from the EPA regulations and did use the original freon formula. The composition change did not contribute to the accident.

This is one that is NOT the fault of environmentalists.