There is a symbiotic relationship that exists between the secondary and the defensive line. The more pressure the front seven can generate on opposing quarterbacks, the more likely the secondary will be able to take advantage of mistakes and create turnovers. Similarly, the better a secondary does in covering receiving options down the field, the longer the front seven has to land sacks, create negative plays or force fumbles. This has become even more true in the modern NFL, which relies heavily on the passing game to win.
While Chris Ballard has mentioned that he believes there are pass rushers to be had in the draft in the middle rounds, I believe that this is a relatively weak group compared to an average draft class.