Manu Smriti as we have today is an interpolated scripture. However, the interpolation defense can not explain all the absurdities in Manu Smriti. So the best way to understand this kind of statement is by invoking Vivekananda.
The Smritis and the Puranas are productions of men of limited
intelligence and are full of fallacies, errors, the feelings of class
and malice. Only parts of them breathing broadness of spirit and love
are acceptable, the rest are to be rejected. The Upanishads and the
Gita are the true scriptures.
The Complete Works of Swami Vivekananda/Volume 6/Epistles - Second Series/CXXIV
We should also remember that Hindu shastra forbids any act even that considered as holy if it hurts the interest of the other.
When can holy acts be done?
If a holy act is against the interest of other members of the society,
it should not be practiced. It is Dharma which is the source of Artha
and even of Kama.
Kurma Purana I.2.54
So the actions prescribed in the above Manu Smriti shloka cannot be actually enforced without violating the advice of the Hindu shastras.
To be fair, Manu Smriti itself asks us to change customs, rules and traditions that are offensive.
However, discard the desire (kama) and material wealth (artha) if
contrary to Dharma; as also, any usage or custom or rules regarded as
source of Dharma if at any time they were to lead to unhappiness or
arouse people's indignation.
(Manu Smriti 4.176)
The existence of such obnoxious shlokas in Manu Smriti suggests that there was a serious degradation in Hindu intellectual standards at that time.