Question

Were critics of WWI anti-American?

Answer 1

Of course not. You have to understand, the government didn't want to join WWI (and they tried many different things to keep them out of WWI), but it was simply impossible to stay out of it. The 3 things that forced America to take action was...
The sinking of the boat Lusitania by a German U-Boat (it had 120 Americans on it)
A message that was intercepted by the British government stating that Germany was willing to give Mexico Texas, AZ, and New Mexico if it attacked the US (A.K.A. The Zimmerman note)
And lastly the sinking of several US ships heading to Britain

Answer 2

So no, the critics weren't anti-American, they simply believed that the US shouldn't have been in WWI, a war all the way across the Atlantic Ocean, were men were led to battle so most good get slaughtered and the few that made it across the battlefield would be gassed.