While in general we don’t encourage conversion, the situation you describe is not so pashut. There is a big problem, especially in Reform, with children of only a Jewish father being raised as Jews and told that they are Jews because “you only need 1 Jewish parent”. Some Rabbeim have held that a child of a Jewish father who is brought up in a Reform shul (and therefore thinks he’s Jewish) SHOULD be steered toward a proper conversion so that they can be legitimately Jewish rather than saying they are but really aren’t. Obviously, if they’re not going to sincerely convert, you do go ahead with it, but you at least get them to know enough to realize they’re not Jewish. Also, some hold that you do try to convert a spouse- they’re already married, might as well attempt to make it legitimate (again, it doesn’t always work, but if it does, that’s much better than the status quo).
Also, it’s a complete myth that a conversion for marriage is automatically invalid. It is automatically SUSPECT, but NOT necessarily invalid.