Many years ago i was driving my brothers first car, a vauxhall nova, while my car was off the road. The exit ramp off the local dual carriageway is a long sweeping left hand bend that loops back round under the carriageway, and is a piece of road that i'd drive everyday. Was driving this nova round there one day and it was clearly a little more greasy/slippy than i expected, half way round i felt the tiniest of twitches/lightness thru the steering wheel and before i could contemplate reacting the back end stepped out. By some miracle there was nothing near me on the road, and instead of opposite locking it to try and hold/correct it, i turned into the skid and the car did a 360 and ended up on the hard shoulder pointing the correct way with no damage.
Having less grip on the rear of a car is extremely dangerous as the above example shows, the steering wheel felt completely fine, and even when it did go onto the slippy patch it just got ever so slightly light. The rear however with less grip, let go and put the car into a spin. Had there been anything beside or behind me i'd have taken it out and probably caused injuries.
Putting grippier tyres on the front specifically so you can utilise their extra grip is even more silly, because it means your likely to push the car even further past the limits of the rears without any feedback from them.