I think the thing to do is to understand why it is that some people are saying that they are bad for you. You might find that those reasons don't apply to you. Or you might find that you don't think they make a good case for them being bad.
That way you will be able to pursue your own intelligent line of training without being at the whim of the vagaries of exercise fashion.
(do you really want to look like most people??)
My understanding is that (like most things) it depends on how crunches and situps are performed.
E.g., for people who do a lot of sitting they tend to have shortened and overactive hip flexors and lengthened and underactive abdominals. This leads to a host of problems (including underactive glutes and lumbar pain). It is natural / easier for these people to use their hip flexors rather than their abs to do sit-ups. Unfortunately this compounds the problem. Not everyone is in this position, though, and other people might well use sit-ups to good effect.
Use the in site search function. There are several really good articles on the function of the core and different exercises that one can do to train the different functions.