It is, however, sobering to remember that when Vietnam invaded Kampuchea in 1979 in order to remove Pol Pot's regime that the Vietnamese were almost universally condemned with the French delegate to the UN at that time describing the notion that "because a regime is detestable foreign intervention is justified" as "extremely dangerous". In fact, if it had not been for a veto from the Soviet Union, there would have been passed a resolution calling upon the Vietnamese troops to withdraw.
During the Rwandan genocide of the 1990's no one moved to intervene and it took the slaughter of Srebnica to move Western governments to act to stall and eventually turn back the Serbian tide in the Yugoslav wars. Even the intervention into Kosovo carried out by NATO later in the decade came without UN sanction and against a backdrop of disapproval from Russia.
Given this situation it appears far from settled that there is any kind of generally recognised humanitarian right to intervention despite the fact that there has, in recent years, been much talk of one. The problem often seems to be that explicit and general recognition of such a right is felt to be a two-edged sword. It is also blatantly evident that states continue to be moved by considerations that are only selectively moral.
None of this is an indication that the French (or someone else) should not intervene in Guinea. The regime there is clearly a danger to its own population on whom it has effectively declared war. However this was just as clearly true for the regime of Pol Pot despite the Western response at the time of the Vietnamese invasion. Perhaps further clarification of the grounds, bases and right of intervention could do with being undertaken?