New research shows that men who had had a heart attack were more likely to die from coronary heart disease when they replaced saturated fats with polyunsaturated fat in margarine
Butter contains a great deal of saturated fat and also monounsaturated fat - these are highly stable. The smallest groups of fat in the butter are polyunsaturated - with more omega 6 than omega 3. The larger proportions of saturated and monounsaturated fats make it more difficult to damage the small minority of polyunsaturated fat. However that minority can still be damaged so it is still important to have fresh butter.
There are so many variables to this because plants oils in margarine are partially damaged by the hydrogenation process. It can be trans fats that are causing problems (not just polyunsaturated omega 6).
Polyunsaturated oils also easily damaged by heat, UV light and oxygen from the air. It could be the consumption of damaged oils that contributes to inflammations. Polyunsaturated omega 6 oils are valuable but should be consumed in their undamaged forms within nuts, seeds, whole grains not be heavily processed.
Omega 3 fatty acids are also polyunsaturated and susceptible to damage so should also be consumed fresh or ideally not hydrogenated.
A balance between omega 3 and omega 6 is also important for health - in controlling inflammation.
Replacing butter (mainly saturated fat) for omega 6 rich plant oils can potentially reduce the amount of damaged oils you are consuming, will increase the amount of saturated fat you are consuming and decrease the amount of omega 6 fatty acids you are consuming.