It remains unclear whether the most present beggars are the ones who are most in need of help. As a result it goes against the concept of effective altruism and can be seen as immoral.
Begging encourages people to act based on feelings and compassion, instead of acting by reason.
People should be allowed to give their money directly based on their own conscience. To criminalize begging would take that right from the giver.
It is not for anyone else to determine the value of an individual's donation to any cause.