When we really hate a thing it makes us sick, and we use this expression to symbolise the utmost hatred of which our nature is capable; but when we know we hate, our hatred is in reality mild and inoffensive.
 Samuel Butler, The Note-Books of Samuel Butler (1912). copy citation

Context

“When we really mean business and are hungry with affection, we do not know that we are in love, but simply go into the love-shop—for so any eating-house should be more fitly called—ask the price, pay our money down, and love till we can either love or pay no longer.
And so with hate. When we really hate a thing it makes us sick, and we use this expression to symbolise the utmost hatred of which our nature is capable; but when we know we hate, our hatred is in reality mild and inoffensive. I, for example, think I hate all those people whose photographs I see in the shop windows, but I am so conscious of this that I am convinced, in reality, nothing would please me better than to be in the shop windows too.” source