Note: there is no evidence that Paine was vegetarian, but his thinking was very influential on those who followed.

Quote:

The moral duty of man consists of imitating the moral goodness and benificence of God manifested in the creation towards all his creatures. Everything of persecution and revenge between man and man, and everything of cruelty to animals is a violation of moral duty. - The Age of Reason

A poem:

CRUELTY TO ANIMALS EXPOSED

Occasioned by a real circumstance

A Pale and wrinkled wretch I saw one day,
Whom pale disease had wither'd half away,
And yet the sad remaining half seem'd curst
With all the mis'ries that befell the first;
While death, impatient to unite the two
Pursu'd him hard, and kept him in his view.

This half-dead wretch with pain and palsy shook,
Beneath his arm a captived kitten took,
Close to his savage side she fondly clung,
And unsuspicious, kindly purr'd and sung;
While he with smiles conceal'd his black intent,
And gentle strok'd her all the way he went.

Without the town, besmear'd with filth and blood,
And foul with stench, a common butch'ry stood;
Where sheep by scores unpitied fell a prey,
And lordly oxen, groan'd their lives away;
Where village dogs, with half the dogs in town,
Contention held, and quarrell'd for a bone.

The crippled wretch to these unpleasing bounds.
His cat convey'd, a victim to the hounds.
To see her living mangled limb from limb,
Tho' scarce alive himself, was joy to him:
So close and slow he crept along the ground,
As if the earth was bird-lim'd all around;
And every ;step so feebly took it's leave,
As if the next would step into the grave;
While ev'ry worm, impatient for its prey,
Cried, Stop him, Stop him, Stop him, all the way.
Yet not one soft relenting thought arose
To bid him spare, but on the murd'rer goes,
Down to the dogs the hapless victim threw,
And clapt his trembling hands to set them too.
Dogs will be dogs, and act as nature taught
Murder with them is merit, not a fault.

A stick I had, tall, knotted, stout, and straight,
Which many a mile had born my weary weight,
Been the companion of my trav'ling cares,
And stood my friend in many strange careers,
With which full many a pow'rful stroke I dealt,
Till ev'ry dog the crab-tree vengeance felt,
And feeling fled--For dogs, like wiser men,
Sleep most securely in an unbroken skin,
Poor puss escap'd-- while Moloch, good of blood,
Like some out-schem'd malicious devil stood,
Convuls'd he seem'd, like one by spells possess'd.
Or he who feels a night-mare on his breast,
And wanting power to move and breath to speak,
Remains in mis'ries till the witchcrafts break.

But fate, which soon or late, all wrongs redress,
Down from the greatest mischiefs to the less,
On Moloch's self the same diversion tried,
The dogs fell foul upon him and he died.

May 1775, Pennsylvania Magazine
Attributed to Thomas Paine, who at the time was the editor of the Pennsylvania Magazine, in "The Life of Thomas Paine, by Moncure D. Conway, first published 1892. Paine was also attributed as the author in "Tom Paine: A Political Life," by John Keane, 1995. (poem and notes sent by David Hurwitz)