Magic and science do not mix. That's why I don't dabble or anything else.
There are many examples other than Newton of scientists who were heavily involved in trying to do magic. Go look up the founder of the JPL and noted Thelemite occultist Jack Parsons, for instance. http://en.wikipedia.org/wiki/Jack_Parsons_%28rocket_engineer...
If you are going to dismiss Dee on the basis of his irrational beliefs, than you must dismiss Newton, Tycho, Kepler and many others as well.