The Imaam of our Musjid is a faasiq. He trims his beard and mingles with the opposite sex.

Answer

Even if the imaam of the Musjid is a faasiq (a flagrant sinner) then too it is compulsory for the males to attend the Fardh Salaat in Jamaat at the Musjid. If nearby there happens to be another Musjid with a pious Imaam, they should perform Salaat in that Musjid. But if all the Imaams are the same, the males have no option but to go to Musjid. They may not perform their Fardh Salaat at home unnecessarily. Those who appoint the faasiq to be the Imaam will get the sin for this haraam appointment.