There are a LOT of great comments from other posters here regarding the social/cultural reasons why the left hates Putin, so I won't address that in this post.
However, something overlooked is the POLITICAL and ECONOMICAL reasons why Putin is hated.
Here's the reality: The "elite", be they GOP, Democrat, whomever, want two things: MORE MONEY, and MORE POWER.
One of the quickest and most efficient ways of securing both of these things is WAR. But war with whom? The American people, by and large, are iPhone obsessed zombies. They are not a war-mongering type. They want comfort and fantasy. War is ugly. They must be goaded into accepting it.
We saw Bush pull it off with Iraq and the fictional WMDs. But we invaded Iraq, there were no WMDs. Of course, we now have ISIS, but how do you kill an ideology? It's very hard build tanks, airplanes, and bombs to kill "lone wolves".
Enter Russia.
Even if you didn't live through the cold war, EVERYONE in America is aware of at least the basic facts. For this reason, a large portion of Americans are still uncomfortable with the idea of a powerful Russia. So Russia makes an easy scapegoat and enemy for the "elite" to get the Americans to hate. Putin is our Goldstein (1984).
If the elites are successful in both convincing the American people/congress into declaring war on Russia OR if they are able to goad Russia into acting "aggressively" enough to justify military intervention, it will accomplish several things:
1. It will pour more money into the military industrial complex.
2. It will (temporarily) kickstart the economy. Note that this is not a REAL economic success. Nothing of value will be produced. The money printed and spent will be by the US Govt, and will go towards weapons we don't need and soldiers to fight and "enemy" who would be better left alone.
3. Putin stands in the way of Globalism. As long as Russia stands strong, the NWO will not be complete.
4. Putin stands in the way of NATO and the EU. Russia is a strong advocate against both, and since Russia borders Poland and the like, Putin stands in the way of the NWO absorbing these countries into it's fold
There are other political/economic reasons, but I think this is a good start.