Mormon's catalog of Lamanite evils continues.
[Thus they were a very indolent people] This phrase flows directly from the assertion that they do not want to work with their own hands. To Nephite ideology, this is the definition of indolence.
[many of whom did worship idols] Mormon could have said that most of them did, if not all. Particularly during his day, the presence of idols would have been pervasive. Certainly the Mesoamerican cities that have been excavated show ample evidence of having certain types of idols. Nevertheless, much of Maya monumental art is not depicting gods, but rather mortals and kings, who were considered semi-divine, but were yet real men. We do see idols large scale idols in later Mesoamerican history, and perhaps there is some development that Mormon witnessed that allowed him to indicate that there were "many" who worshipped the idols rather than "all." Certainly, whether or not there was an idol involved, they worshipped multiple foreign gods.
[and the curse of God had fallen upon them because of the traditions of their fathers] Mormon applies the curse to them generically, and does not really state what the curse is. From his next phrase, however, it appears that he relates the curse to a distance from the true religion, since they appear to be redeemed from the curse with conversion.
[notwithstanding the promises of the Lord were extended unto them on the conditions of repentance.] Even though they carry a curse from God, they may be redeemed. Certainly the implication is that they are also redeemed from the curse. Thus whatever Mormon conceived as their curse, it was something that could be removed though repentance and acceptance of the gospel. One of the aspects of the curse was the required separation of the Nephites and the Lamanites, with the particular prohibition of marriage. When a Lamanite was converted, he became a Nephite, and we hear of no continuing marriage prohibition. Indeed we will see converted Lamanites living in Nephite lands and becoming completely accepted members of Nephite society. Thus this curse was entirely removed through conversion.