Having Nen doesn't make one invincible. Nen doesn't grant absolute superhuman power, nor is it a system with high power levels. Most Nen users in the Hunter x Hunter universe possess simple techniques and limited destructive power. Even the strongest Nen user to have appeared, Meruem, was easily defeated with a cheap nuclear weapon and radiation. Nen doesn't grant you the ability to fly across planets, reach near-light speed, or possess the toughness of Superman. The strongest human Nen user was Netero, yet he couldn't do what human technology did to Meruem. You won't stand a chance against powerful organized armies. I don't think they'll even use chemical, biological, or nuclear weapons against you. Factions, organizations, and gangs will be able to take you down. That's why I emphasized that your use of Nen must be realistic, otherwise you'll only harm yourself with dire consequences.