Do you need a skimmer in a tank or can you get away without using one?...
If your looking for strictly s yes or no answer, the answer must be no. You don't need a skimmer. However, on any tank larger than about 30 gal, a skimmer is highly desirable, to the point where I would not run a larger SW tank with out one.
If you doubt that a skimmer works, simply take a look at all the glop it removes from the system. Consider too that this material is being removed befor the biological filtration needs to deal with it.
As for "other people saying you don't need one because it's takes away all the good stuff for the filter feeders", yes some of this does occur to some extent. A skimmer will remove most fine material, but the benefits far outweigh the downsides.
There are a lot of poorly designed skimmers on the market, especially on the low end. Some are out and out junk, Before you buy, ask about it here first. Expect to spend some money on something decent, and as usual I recommend getting top quality equipment. Note that top quality does not mean most expensive.