What is the "downside" to extensive use of synthesized nitrogen-containing fertilizers?

There are several "downsides" to extensive use of synthesized nitrogen-containing fertilizers; it contributes to algal blooms and dead zones in bodies of water, nitrogen is usually considered as a highly effective and economical fertilizer. However, the repeated use of the chemical can cause an imbalance in the pH of the soil, eventually leaving it unusable for growth of any kind.