As regards selling at a loss: if you do this with the aim of destroying or damaging your competition, so that in the future you may enjoy greater profits e.g.

As regards selling at a loss: if you do this with the aim of destroying or damaging your competition, so that in the future you may enjoy greater profits e.g. due to having a monopoly, then it is bad for society - the word immoral is not unreasonable. There exist laws that try to prevent this type of behaviour, because of the public harm it causes.