The Fed is often criticized as an institution because it was first established by a small group of Bankers after several banking crises in the early 20th century, and all FOMC members are appointed, not voted by the people directly (c.f. indirect democracy). My personal take is that Congress would be much less efficient and effective in "managing" the value of our dollar. Besides already showing its incapacity to pass legislation on a decent amount of subjects in the past several years, leaving currency and interest rate management to voted officials would increase inflationary risks and open a bag of worms in terms of moral hazard. The Fed isn't perfect, but I trust seasoned bankers and researchers who come from the private sector to run this part of our affairs (Trump fans should too I guess).