I will make one thing totally clear: No blood is 100% safe. There is always going to be a risk of a mistake, or a new disease that they don't have the technology to screen for. And there is a chance of type mismatches of various factors. Taking a blood transfusion is not something I would want to mess with. Unlike playing with a Ouija board or decorating for Christmas, using blood for frivolous situations is not wise.
However, there is a point where the benefits outweigh the risks. If a child's life is at stake, that for sure outweighs the risks. There is going to be a chance of getting AIDS because of a stupid mistake in screening. But without the blood, the risk of dying or having serious adverse effects from not dying is far greater, if not 100%. And there is the cost of the blood itself--frivolous blood transfusions will deprive people that really need blood. Here is one area I highly recommend doing cost/benefit analysis on a case by case basis: If the benefits outweigh the total costs, then the blood should be used anyways, even with the risk of getting AIDS or hepatitis X.