The temptation of trade slowly forced the colony from this high moral ground. New England ships were early found in the West Indian slave-trade, and the more the carrying trade developed, the more did the profits of this branch of it attract Puritan captains. By the beginning of the eighteenth century the slave-trade was openly recognized as legitimate commerce; cargoes came regularly to Boston, and "The merchants of Boston quoted negroes, like any other merchandise demanded by their correspondents."[18] At the same time, the Puritan conscience began to rebel against the growth of actual slavery on New England soil. It was a much less violent wrenching of moral ideas of right and wrong to allow Massachusetts men to carry slaves to South Carolina than to allow cargoes to come into Boston, and become slaves in Massachusetts. Early in the eighteenth century, therefore, opposition arose to the further importation of Negroes, and in 1705 an act "for the Better Preventing of a Spurious and Mixt Issue," laid a restrictive duty of L4 on all slaves imported.[19] One provision of this act plainly illustrates the attitude of Massachusetts: like the acts of many of the New England colonies, it allowed a rebate of the whole duty on re-exportation. The harbors of New England were thus offered as a free exchange-mart for slavers. All the duty acts of the Southern and Middle colonies allowed a rebate of one-half or three-fourths of the duty on the re-exportation of the slave, thus laying a small tax on even temporary importation. The Act of 1705 was evaded, but it was not amended until 1728, when the penalty for evasion was raised to L100.[20] The act remained in force, except possibly for one period of four years, until 1749. Meantime the movement against importation grew. A bill "for preventing the Importation of Slaves into this Province" was introduced in the Legislature in 1767, but after strong opposition and disagreement between House and Council it was dropped.[21] In 1771 the struggle was renewed. A similar bill passed, but was vetoed by Governor Hutchinson.[22] The imminent war and the discussions incident to it had now more and more aroused public opinion, and there were repeated attempts to gain executive consent to a prohibitory law. In 1774 such a bill was twice passed, but never received assent.[23]