What's so terrible about saying "the system is rigged"?

[Gothmog]

2. Trump used this bogus claim to great effect

Sanders had no chance of being the nominee after Super Tuesday but continued his campaign which hurt Clinton. Here is a good example Sanders really hurt Clinton I am still mad at the number of times that trump used Sanders' claims against Clinton. Sanders' baseless charges that the system was fixed and rigged were used by trump to great effect and hurt Clinton http://www.huffingtonpost.com/entry/rigged-system-donald-trump_us_5855cb44e4b08debb7898607?section=us_politics

And if Sanders’ rhetoric during the primaries started that stew simmering with his talk about the system only working for the rich, Trump brought it to a full boil with his remarks blaming undocumented immigrants and trade agreements that he claimed were forged as the result of open corruption.

I think he was able to thread a certain toxic needle. But he did win, and we’re all going to pay the price.
John Weaver, aide to Ohio Gov. John Kasich’s presidential campaign

The underlying irony for those who sought to end what they perceived as corruption is that they may well have elected a president whose record through the years and whose actions since the election signal it could be the most openly corrupt administration in generations.....

And if Sanders’ rhetoric during the primaries started that stew simmering with his talk about the system only working for the rich, Trump brought it to a full boil with his remarks blaming undocumented immigrants and trade agreements that he claimed were forged as the result of open corruption.

Sanders' bogus rigged process claim hurt a great deal