Discussions of sinlessness are hindered by broad-brush treatments of the topic. It is important to make a distinction between sinlessness and perfection.
Jesus commanded us to be perfect:
Therefore I would that ye should be perfect even as I, or your Father who is in heaven is perfect. (3 Nephi 12:48)
His commandment perplexes many who consider their sinful state and wonder how that could ever be. Their bewilderment is not just due to a lack of faith, but also a conflation of the difference between perfection and the path to it.