What is ironic about lines 69 and 70? What evidence supports this irony? A modest proposal

Please quote these lines so I know exactly the ones you mean. Counting lines can produce a different number depending on where you are reading it.

" That the remaining hundred thousand may, at a year old, be offered in sale to the persons of quality and fortune, through the kingdom, always advising the mother to let them suck plentifully in the last month, so as to render them plump, and fat for a good table. A child will make two dishes at an entertainment for friends, and when the family dines alone, the fore or hind quarter will make a reasonable dish, and seasoned with a little pepper or salt, will be very good boiled on the fourth day, especially in winter". This is the lines