People like what Punisher stands for and that's why he is so popular. 95% of the people putting his Emblem up haven't read a single comic book other than a page someone shared on Facebook.
When you are military, you can tell that there is no justice in anything in war. War is inherently unjust. The mechanisms of justice can only exist in peace, and in the worst cases, it looks like even God might have abandoned man. In such a case, where justice can only come from power, and power can only come from the barrel of a gun, then the only justice is to kill the bad guy before he makes another victim. Bringing his unrelenting terror and slaughter to an end is the closest thing to justice you can achieve. As such, this is the mentality of the Punisher, which is why so many sympathize with it.
That's basically the entire US military.
It's from that kind of cynical view I mentioned. "Man's Wrath" rather than "God's Wrath". When there can be no real justice, and there are no real heroes, all that can be done is punishment.
When you are military, you can tell that there is no justice in anything in war. War is inherently unjust. The mechanisms of justice can only exist in peace, and in the worst cases, it looks like even God might have abandoned man. In such a case, where justice can only come from power, and power can only come from the barrel of a gun, then the only justice is to kill the bad guy before he makes another victim. Bringing his unrelenting terror and slaughter to an end is the closest thing to justice you can achieve. As such, this is the mentality of the Punisher, which is why so many sympathize with it.