Buying stocks in the stock market when their price is falling is almost always a good idea.Almost not always.The idea is to buy low,sell high.For example Apple AAPL tomorrow will release the quarterly earnings and results.For now it is down at 97.33 -1.35%.
If earnings are good then an up move is very likely.But there is always the risk of earnings not meeting expectations.In any way buying at lower prices stocks seems a very reasonable investing strategy.