Why should you not use Parallel 5ths in Harmony and Counterpoint exercises?

Parallel fifths are an example of poor voice leading, especially in chorales. The melodic lines should be easy to sing. Lines composed using parallel fifths are incredibly difficult to sing and are not contrasting in the overall field of the piece. It is not an independent line. J S Bach almost always avoids parallel fifths in voice leading, opting for other structures. Parallel fifths often create a 'bare' sound, which draws one's attention to this element. In the end, avoiding the sound of parallels is part of the aesthetic of tonal music and they should only really be avoided for the same reasons as unprepared dissonances. If you write a bass line first that avoids parallels, you are much less likely to end up with them in the inner parts.