Why is rent-seeking so costly to growth?

NY Times today has a sobering article about the concern of talented students flocking to finance sector. Influential economists in both Uni. of Chicago and Harvard Uni. found an interesting impact on GDP from the majors of college students. 10% increase of engineering majors will lead to 1.25% increase of GDP. 10% increase of law majors will incur 0.65% decrease of GDP. (Table VI inhttp://www.nyu.edu/e…/user/bisina/murphy_shleifer_vishny.pdf)    http://www.nytimes.com/2015/04/12/upshot/why-a-harvard-professor-has-mixed-feelings-when-students-take-jobs-in-finance.html?abt=0002&abg=0