I'll get right to Lew Rockwell's excellent treatise:

All rational Americans agree that we shouldn't get involved in the Russia-Ukraine War. The neocon warmongers with brain dead Biden as their figurehead want to destroy Russia, and they are willing to risk nuclear war to do it. But this doesn't negate what I've just said. These monsters are anything but rational. But speaking of monsters leads to another question. Everybody knows John Quincy Adams's line: "America goes not abroad in search of monsters to destroy." Is this the reason we should stay out of the Ukraine war? Is Putin a monster, bringing death and destruction to innocent people, but someone whose actions we have to ignore because it's too dangerous to act against him? People who say this don't get what's happening. Putin is a rational statesman, with legitimate security interests and the supposed hero Zelensky is a dubious character.

Why do people think otherwise? One reason is the charges of Russian atrocities in Bucha. These charges are just that "charges". Fake atrocity claims have often been a way to inflame people to support war, and the Bucha accusations are the latest example. Christopher Roche, who isn't pro-Putin, explains why we shouldn't fall for it: "The reports and photographs showing an apparent massacre in Bucha, Ukraine, are truly terrible. They are reminiscent of the atrocities used to galvanize Western opinion during Yugoslav Wars of the 1990s, when the Srebrenica Massacre and the Siege of Sarajevo were seared into Western consciousness.