If you make controversial statements in public you must expect a reply whatever your personal circumstances.
Like you I disapprove of hateful personal abuse, but Farage did not do that, so I can not agree that this is some "new low."

Farage's view Cox objected to is widely held in Germany and perfectly reasonable.
Merkel was criticised at the time for allowing in without checks around a million "refugees," who were in fact overwhelmingly young (military age) men, on the grounds of the security threat posed.
The criticism could only intensify as Germany suffered terror attacks, and support for Merkel has plummeted.