Cooley has a negative rep because it has relatively low admissions standard. Their student numbers are among the lowest in the country, and they compound this image problem by creating their own rankings that place them in the top 15-25. This makes them the target of frequent derision.
However, Cooley is in fact fully accredited, and what you'll actually learn at Cooley probably isn't much different than what you'd learn anywhere else. Your textbooks are probably all the same, and the profs are probably all from top schools.
Probably most importantly, it is still possible (though not as easy) to be successful from a school like Cooley. I've only met a handful of Cooley grads, but two were millionaires, having won multi-million dollar verdicts. I sure as hell didn't look down on them.
Bottom line, if you attend a school like Cooley, your academic life may be more stressful, and you'll probably have a much harder time finding work after graduation than if you attended a top-tier program. However, if your dream is to be an attorney, and you don't fare well on the LSAT, Cooley is one viable option for realizing that dream, as long as you're willing to do the extra legwork to become successful.