Whatever the opinion, surnames have been used as first names for centuries and continue to appeal to many. Today's name was chosen due to its aristocratic connections (no surprise there) and its long history.
As a surname, Sinclair (sin-KLER ) has been used in England and Scotland as far back as the Norman Conquest in 1066. Unsurprisingly, therefore, the name derives from a Norman town called Saint Clair. The town was given its name due to its many churches dedicated to St Clarus, a monk who is said to have performed a number of miracles. The Latin Clarus - used as a masculine name in its own right - means 'illuminated', 'clear' and 'illustrious'.
One of the positives of using a name such as this is its flexibility. There are a number of acceptable spellings, including Sinclaire, Sinclar, Sinkler, Sencler, Synclair, Seintcler, Sancler and St Clair, but Sinclair remains the most common. Its flexibility extends to gender. Predominantly it has been given to boys, and the BMD records show its usage from the late 1830s up to the 1960s. But one does find it being given to girls also. Its similarity to Claire, Clara etc. could very well tip it into female territory. On the negative side, the name does include the word 'sin', but it should be noted that it is, of course, a shortening of 'saint'.
Furthermore, it is the surname of the Earls of Caithness. The earldom goes as far back as 1334 when it was created. Still a bit iffy on the whole thing? Perhaps a quote by Sir Bernard Burke can capture your interest. He stated that 'No family in Europe beneath the rank of royalty boasts a higher antiquity, a nobler illustration, or a more romantic interest than that of St. Clair.' There is also a castle named after the important family, and the Sinclair clan still exists today. With all of this, Sinclair is a name full of history and of strong Scottish connections.