Does working abroad cause less unemployment? Or is it actually harmful (directly or opportunity cost)?
On remittances:
It is not unusual to hear about income being sent home by, say, US immigrants. However, the product of their labor and the side effects of their intellectual capital, sometimes called positive spillover, do not occur in the home country.  As such, they are not as beneficial to the home country as some counterfactual world where an equally profitable job existed at home. The immigrants are then beneficial to the host country.  The remittances still benefit the home country, however, and are particularly important when no employment is available at home.
On unemployment:
Broadly, immigration does not appear to have much of an impact on the unemployment in the host country. Or at least, something happens which masks that effect and makes it tremendously difficult to measure.  There has been a lot of controversy on this study but it helps highlight a lot of the issues if you take the chain of papers and responses seriously: https://www.jstor.org/stable/2523702?seq=1#metadata_info_tab_contents
On the type of people immigrating:
&quot;Are the ones going abroad necessarily like money-hungry people who do not love their country or something.&quot;  This isn't really the type of question economists answer. Everyone is money-hungry and equally self-interested, by default, and that is fine.  This helps (in some ways) avoid stereotyping immigrants. You may want to open another question about the types of people who like to immigrate.