Why is this still an issue in the fitness industry? Stretching what? muscle, connective tissue? I still wonder how many FT’s know why a muscle has tension and what happens to a muscle and its connective tissue when you “stretch” it? Did your certification include a study on Neurology? Love to hear your opinion?
The better question would be to ask not if you should or shouldn’t, but what type of stretching to do and when. Always warm up before stretching or at the least gradually increase your stretches as your muscles warm up to the activity. Before exercise, more movement based stretching is beneficial such as ballistic stretching, because you also want to wake up the nervous system and prepare the body for activity. It has now repeatedly been shown that static stretching before an activity will actually decrease performance.
Post workout would be the time to use static stretching as this helps to relax the muscle and calm the nervous system.
Granted there are a lot of other systems out there and i only mentioned 2 of the more widely/popular forms of stretching, but the important part is to improve the body for activity and/or stay flexible after activity. There are more and more research papers out there touting benefits to stretch and guideline, you just have to be patient and search NSCA journals and maybe PUBMED.org.