Once we go further than that the west can then be seen as picking winners and losers in the conflict and it will be construed as more western intervention in Arab affairs. If the rebels are victorious they will need to have credibility in order to establish government and build international relationships. If they are seen as being beholding to the west I think that this will be very difficult. (That is assuming that we in the west don't wind up getting involved politically which would make a bad situation worse IMHO). AS I said earlier it is important that this be viewed as an internal matter and not one that is being dictated by the west.
All very true. However, I don't think the current escalated intervention can be construed as picking a winner. We are picking a loser but one who everyone else in the arab world thinks is a loser. If the West only concerns itself with preventing large scale violence and keeps out of the political process I think they will come out looking fine.
Right now there are a number of countries in that part of the world whose governments are being seriously tested. By over stepping the mark in Syria we might cause other rebel groups to assume that we will step in to any similar situation over there. (Also, with what we are doing in Syria I think it is also fair to ask why we weren't in Sudan.)
Or why we haven't stepped in to stop genocide throughout Africa.