On the day the Prophet was born, abu lahab was so overjoyed that he freed the slave girl who brought him the good news, and for that reason, his punishment is lessened on every Monday. On the other hand, abu Bakr never celebrated the birth of the Prophet in the way people do today, by gathering on one day out of the year and singing poems and sending salwat. I don't think Salafi-Muslim has given a proper representation of these facts, though. That fact that even a kafir like abu lahab is rewarded for being happy about the birth of the Prophet should be an encouragement to us. How much more will be the reward of the mu'min who is happy for his birth ? Abu Bakr did not celebrate mawlid on one day out of the year; he celebrated it every day of his life. As for gathering and singing the praises of the Prophet , this was sanctioned by the Prophet himself, as Hassan bin thabit was given a platform in the masjid nabawi to stand and sing the praises of the Prophet while the people were gathered there. I am not talking about celebrating by men and women gathering together and having a feast, but by simply gathering throughout the year without fixing any date to commemorate his birth and his life and death, learn about his sunnah, and send salah and salam to him. I don't usually go to gatherings like that in rabiul awwal, but I don't go out of my way to criticize those who do if what they are doing does not contravene the shariah.