The Economist took a strong stand against streetcars:

• Proponents of streetcars note that they bring prosperity and development. Areas in Arizona, Washington D.C., and Texas are all considering implementing lines.
• However it’s much cheaper to build a bus line. The capital cost per mile of streetcars can go up to $75 million, while the equivalent amount for buses is just $30 million.
• Moreover buses are able to move around obstacles, while streetcars are stuck until the obstacle is removed. Thus more often than not streetcars adds to congestion rather than alleviate it.
• Streetcars are also slow, and typically have more frequent stops over walkable distances.
• Developers seem to like building them because they’re ‘sexier’ than buses and because they attract tourists. All in all though the benefits aren’t worth the costs.

Read more of the argument, find out why they work better in Europe, and see details of the cost-benefit analysis over here.

Source: The Economist