Corporate Mergers - positive or negative for Economy?

The near-permanent dealmaking has reached frenetic proportions during the past 20 years. Are all these mergers really necessary to sustain a growing economy that benefits employers and workers alike? Is Anti-Trust really up to the challenge of assessing all transactions? Should there be higher tax burdens imposed?
CITI: 'One of the scariest charts to look at' could create major concerns about the market