No physical harm
I agree with dr. Mcmullen.
Perhaps you have an oral fixation and feel soothed by ingesting your snot. On the other hand in western cultures, picking ones nose and eating the snot may give one the pleasure of doing something that is considered taboo but which is not ethically problematic. If you do it in public, others may react negatively. Ingestion of snot isn't harmful but overpicking can be.