I myself don’t say that receiving Holy Communion on the hand is wrong, but simply that receiving in the tongue is better in two ways, and helps with two things. Those two things are reverence for the Eucharist, and lowering the possibility of committing sacrilege.
The reason that it helps with reverence is that it is an outward and inward sign of humility and holiness. There are many times that people who receive CITH don’t examine their attitudes towards receiving the Eucharist. A couple of good acquaintances of mine who used to be extraordinary ministers of holy communion have all at one point encountered people receiving the Eucharist with a dead look. They receive as if they didn’t even know what they were receiving. Now this does not mean that everyone who receives kneeling and on the tongue had to examine their conscience and attitude towards receiving, but it is easier to do so. I personally think that taking that extra step towards kneeling and receiving in the tongue helps with acknowledging the True Presence of the Eucharist, as well as helping with humility.
The second thing is that receiving CITT while kneeling also helps lower the possibility of sacrilege. I don’t know how many people have seen this, but two people that I know who have worked with the Eucharist as extraordinary ministers, have both said that many people commit sacrilege with the Sacred Host. There are two main ways that this has happened. The first way is simply that people have dropped the Eucharist while trying to receive in the hand. The second way is a bit more disturbing. Many people have walked away with the Eucharist outside of Mass. This could be done incidentally, but it can also be purposely. This includes sorcerers and witches ( I am being serious), have walked off with the Eucharist and have committed disturbing things with it, as a means of mocking the host.
Now just realize the fact that Pope Emeritus Benedict XVI has himself only given the Eucharist to people, if they were kneeling, and if they were receiving in the tongue. Second of all realize the fact that it was only during after the 60s that people started to receive in the tongue. There is anonymous consensus from the older folks in my family that we ought to receive in the tongue.
Lastly just because the church allows for something does not mean that you ought to do it. The church allows people to receive communion two times a day, I only take it once. Why? Because I feel that we ought to show reverence towards the Eucharist and taking it constantly sacramentally could be an abuse.
Why then did Moses command to give a bill of divorce, and to put away? He saith to them: Because Moses by reason of the hardness of your heart permitted you to put away your wives: but from the beginning it was not so. ( Mathew 19:8)