What is the ruling on a man praying at home, under the pretext that prayer in mosques is not obligatory in Western countries?

The preponderant view is that performing the obligatory prayer in congregation (jama'ah) is a duty. Whoever prays at home without a valid excuse misses out on a great reward and commits a sin. There is no difference in this regard between Muslim lands and other lands, as the texts do not differentiate between one place and another. Rather, establishing the congregation in non-Muslim lands is even more emphasized for the sake of demonstrating the religion.