The plot line of two heterosexual men getting married leads to hilarity. Okay, not really. The marriage of the two straight men does allows the writers to incorporate into the show an endless and tiresome stream of straight men acting like stereotypical gay men jokes. Alan, the more effeminate of the two, gets the bulk of those.
It should be noted that Two and a Half Men isn't the only show that incorporated a straight same sex couple getting married. Several years ago in The New Adventures of Old Christine, Julia Louis-Dreyfuss' character married Wanda Sykes' character, Barb, to help her avoid deportation. Although Sykes in real life is a lesbian, Barb was straight.
The plots of the two shows are typical Hollywood in dismissing the importance of the institution of marriage and the personal and legal commitments involved in entering such a union. But probably unbeknownst to politically tone deaf writers and actors (Cryer, Kutcher, Louis-Dreyfus and Sykes are, after all, on record as supporting same sex marriage) the shows' story lines actually denigrate the struggle hundreds of thousands of same sex couples have endured in their fight to be able to marry.
I don't think anyone can argue that advocates of same sex marriage have not been sincere in their push for same sex marriage. Unlike Hollywood, those advocates approach the institution of marriage with a respect for the legal and moral obligations it represents. It is exactly because of their respect for institution of marriage that they want to partake in it. Hollywood mocking marriage does not help that cause.