This is Horace, "Carmina," III, 3:
Justum et tenacem propositi virum,
Non civium ardor prava jubentium,
Non vultis instantis tyranni ...
Which means, more or less:
The just man who is resolute
will not be turned from his purpose
either by the rage of the crowd or
by an imperious tyrant.
"Non civium ardor" in this context would mean "not by the rage of the crowd."
Here is Robert Browning's take on Horace's concept:
http://en.wikisource.org/wiki/Instans_Tyrannus