Nothing is "wrong" with allowing multiplier credit for in state counties for in state stations.  Some QSO parties do exactly that.  What it does, however, is change the character of the QSO party.  Activity on the higher bands is significantly decreased, thereby reducing activity from DX and farther away US stations.  Activity on low bands is increased and often occurs during daylight hours between in state stations who are hearing only each other.  That keeps these stations away from the higher bands.  There will be a lot of in-state stations who go around calling other in-state stations for county multipliers and never call CQ, thereby never giving out-of-state stations a chance to work them.

So, we have chosen in FL, GA, SC, TN, AL, etc. to be more outward looking in our QSO parties.  We allow the state to count as a multiplier for in-state stations, but in order to get more than one mult (or one mult per mode), in-state stations must work out of state stations, thereby resulting in more activity  on the higher bands and more QSOs with DX and west coast US stations. This should not necessarily reduce low band activity (except in FL which does not include 80 or 160M).

73, John, K4BAI.