Pricing your work too low is harmful. Simple as that. The question here is how and why is it so harmful?
Development is a skill, it’s profitable to both you and your clients and has value to everyone who accesses or holds the end product. Finding the right clients and such is a task of it’s own but it’s something that is manageable, however there are ways to find clients, don’t let underselling yourself be the go to.
When underselling yourself, you are damaging your own personal reputation by making the value of your work appear minimal.
When you price a project lower than it’s value you are essentially displaying yourself and your brand as being low value and cheap. In contrast to other developers, clients may see you to be unreliable or expect less of you and therefore go elsewhere to find someone who can best fulfil their needs.