Most people dislike it because it can be categorised as Spam, It sometimes turns into rule breaking, and it bothers other users. They are called mate beggars because that is what they do, they beg. I recently watched one, who followed someone around, constantly spamming, "Wanna be my mate" Yes, some are decent, but there actually aren't that many good ones, at least as far as I have seen, and as far as the community seems to have experienced. Some get nasty if you turn them down, some are just creepy and some do it to break rules (AKA the no buttswinging/mating/raping rule.)
And Mate begging has been termed ever since the game began, it is just that recently it is coined more often, and in a more broad way than before. Now any one who is just looking for a mate is termed a mate beggar, when really they are not. A true mate beggar is someone who spams and bothers and irritates everyone in a map in their constant crying for a mate. They follow people constantly asking to mate despite being told no. If that is what you are doing then yes, you are a mate beggar, and people are going to be irritated by your behaviour. But if you are not spamming the chats with "wanna be my mate" or following people, whispering random people and generally bothering EVERYONE in your vicinity, then you are truly not a mate beggar and it is a case of people over reacting. Now just asking to roleplay with a specific gender character can have people screaming mate beggar at you.
I do not think people have mate beg should get off the game, nor the opposite, and the "antimate beggars" should get lost, I just think BOTH parties need to calm down. The mate beggars for going to extremes just to find a mate, and the "antimate beggars" reacting to even the SLIGHTEST hint of looking for a mate.