It's not really either. There's no real justification for a travel ban, still, because it's been shown in Nigeria and Senegal that the disease can be contained if it spreads to other countries (incidentally, where were the posts about that piece of good news?). On the other hand I can see that governments in other countries may feel under some pressure to be seen to take action to protect their citizens, and doing so is not really discriminatory to other nations (or at least, it is but not in a bad way).
It largely depends what other action Australia takes to combat the disease. A major worry should be that various nations close their borders and think this is somehow all the action they need to take: "If it doesn't come here it's not our problem". The slow response to the crisis as it grew early on shows the danger of this, for example.
If the Australian government also takes action to combat the disease in Sierra Leone at the same time as denying travel from that country, then there's less of a problem. If, on the other hand, it does nothing else, then this is a bad attitude to take and deserves to be condemned.