what can/should each individual jew do, to get rid of intermarriage between jews and forbidden people, from this planet?

Great- that's very important- especially for people within your own family, with whom you have that much more of a chance of influencing. Google: aish hatorah break intermarriage, and you'll find several articles on the topic. Also Google: Aryeh Kaplan break intermarriage also see: https://www.simpletoremember.com/vitals/HowToPreventAnIntermarriage.pdf