The best argument for avoiding US stocks is simple: valuation. Using the Shiller PE Ratio (price divided by a 10 year lookback at earnings), domestic equities trade for 29.9x earnings versus a long run average of 16.7x. The last time they were this expensive was early 2002, or 15 years ago.
http://www.zerohedge.com/news/2017-03-02/last-time-us-stocks-were-so-expensive-happened
Realist - Everybody in America is soft, and hates conflict. The cure for this, both in politics and social life, is the same -- hardihood. Give them raw truth.