One opinion:
You must use a balun
to balance your dipole

From: ran@daneel.rdt.monash.edu.au
Date: March 28, 1995
Original source: Usenet's rec.radio.shortwave

Gary Thorburn (thorburn@.xyplex.com) wrote:
By feeding the antenna with properly grounded coax you get the benefit of a shielded lead-in, which will reduce electrical noise pickup from near your house. Its usually signal/noise ratio, not just signal strength, which is important.

This is true only if everything is connected properly. You cannot just connect co-ax to a dipole and then to your receiver and expect it to work properly. A dipole is a balanced device, co-ax is an unbalanced feeder and the inputs on most modern receivers are unbalanced. You cannot just mix balanced and unbalanced configurations without a balun.
Consider that the signal induced in one element of the dipole is 180-degrees out-of-phase with the signal induced in the other element. A balun is required to reverse the phase of one of the signals so that they are additive. Assuming the use of twin-feeder line from the dipole to the balun it follows that any noise (or signals) picked-up by the feeder will be in-phase between the two lines and will, thus, be effectively cancelled when the phase of one of the signals is reversed.
If you do not use a balun you end up with just a random-wire antenna because the signal from one element of the dipole is just sent straight to ground and contributes nothing. And if you use co-ax from the dipole to the receiver without using a balun you can get significant capacitive losses.
Many SWLs find that a "dipole" often gives no improvement or even inferior results. The reason is usually because a balun has not been used.
There is a great deal of misunderstanding concerning the function of a balun with many regarding it as just an impedance-matching device. A balun may well match impedance but it does not have to - it can easily have an impedance ratio of 1:1.
What is important is that it matches balanced to unbalanced lines. After all, balun is short for "balanced-to-unbalanced"!