If there is one thing in life that is sure it is this. No one is born knowing how to dance. We all have an inner sense of rhythm and quite frankly some have it and some simply do not. It is true that not everyone is meant to dance competitively and some will never refine their skills enough to make their way out of the mosh pit. However, there are those who have that inner sense of balance and rhythm. With proper instruction and the right inspiration these people have the potential to become phenomenal dancers.
Learning how to dance is a process that works differently for different people. Some learn best by one on one instruction. Others manage to learn simply by watching others dance. Some require a little bit of competition in order to properly motivate themselves to push their limits and really give dancing their all. The good news is that there are dance lessons and classes that are appropriate for all different learning needs when it comes to dance.
That being said, in order to dance on a competitive level it is quite likely that you will need to incorporate a little bit of all different methods of teaching and learning for the best possible results. There is nothing wrong with watching others dance and learning and deriving inspiration from the moves they make. You can also discover flaws, weaknesses, and mistakes by watching others dance and learn from those as well.
That being said, you will never learn as much from merely watching other dancers or instructions on a video tape as you will in a classroom or one on one environment. Dance is fluid and there are certain technicalities to the steps but there are other things involved that mark the difference between a dancer with some degree of technical skills and a truly great dancer. Some things have to be pushed and prodded from within you and only a qualified instructor can really accomplish that.
The thing is most, who want to be dancers, should not settle for simply learning how to dance. They need to learn how to feel the music and use the music and their bodies to tell a story. That is what dance is about. Not the execution of even complicated movements. Dance should be an emotional outlet more than anything else. This is the way dance has been throughout history. It is only in the last century or so that we have turned dance into a sport rather than an art form and it has lost some of its potency as a result. Those who truly understand that real dance is delivering a message rather than delivering movements however are the successes that simply can't be matched.
If you wish to learn to dance, you need to carefully consider your reasons for doing so before deciding on your method of learning. I strongly recommend a little of all the different methods. One thing to keep in mind however, is that if you learn from more than one instructor you will be chided for needing to unlearn bad habits. It's an ego thing I believe. Most instructors prefer rank novices so that they do not have to 'unteach' any bad habits. Otherwise, you should choose the instructor that you feel will not only teach you how to dance but also encourage you to dance to the fullest of your potential. Those are a little more difficult to come by.