How do you deal with a Muslim who considers a certain issue permissible while you consider it forbidden, such as the permissibility of photography or its impermissibility, or the permissibility of holding a wedding that includes female voices and singing or its impermissibility, or the permissibility of combining prayers while resident or its impermissibility?

Differences are of two types: one is permissible and considered, which is what the evidence can accommodate and what even a single scholar holds. In this type of difference, there is wide latitude, and one does not declare the dissenting party misguided or sinful. What is required in this type of difference is scholarly discussion with the aim of reaching the preponderant view, for in matters of ijtihad (independent reasoning), one does not denounce the mujtahid or their follower with the same vehemence as one would denounce forbidden acts. Rather, it is legislated to gently clarify the preponderant view therein.