The 19-year-old took his views about the war a step further: He's fighting in it, on the Ukrainian side.
Under pressure from the authorities over his activism, Valentin fled to Ukraine in January and joined the controversial Azov Battalion, a volunteer militia that has played a prominent role in the fighting against Russian-backed rebels in the Donbas.
"When I came here, I had two choices: to live in Ukraine as a refugee or go to the war," he told RFE/RL's Russian Service.
The latter was an "obvious choice," he said by telephone from Mariupol, a strategic Ukranian port city that lies west of the front line in the Donetsk region.
It is coveted by the rebels and seen as a key potential target should they attempt a major new offensive, despite a shaky cease-fire in place since February.
In a second telephone interview with RFE/RL, on June 12, Valentin said he has taken part in several military operations against the separatists near Shyrokyne -- a scene of fierce fighting east of Mariupol -- and Hranitne.
Both towns are at the edge of rebel-held territory.
The conflict in eastern Ukraine has killed more than 6,500 people since April 2014.
Most Russians who have fought in it have done so on the side of the separatists.
President Vladimir Putin denies Moscow has sent troops into Ukraine, despite mounting evidence, such as fresh soldiers' graves in Russian towns, and claims any Russians fighting in the war are there of their own volition.
Valentin's journey to Ukraine started slowly and culminated quickly.
Last year, he took part in antiwar rallies in Krasnoyarsk, one of the sites of demonstrations held around Russia to protest the conflict and Russia's involvement.
Many protesters were people who rejected the Kremlin's narrative about the crisis and conflict in Ukraine, believing that Russia has both provoked and participated in the fighting.
"There were many people who supported Ukraine, but for most it was only passive support," said Valentin, who did not stop at attending rallies.
"Me and my friends would hang Ukrainian flags and posters around the city," he said.
"The photos of an anti-Putin banner we placed on a bridge in central Krasnoyarsk became very popular on the Internet."
In January of this year, Valentin discovered that his actions had caught the attention of the regional security services when he got a phone call from an antiextremism officer.
"He told me, 'Valentin, come to our office. We need to talk. It's very serious,'" he said.
"When we met, the first thing [the officer] told me was: 'We know it was you.'"
Valentin said the authorities accused him not only of hanging the banner on the bridge but also over an incident in which a World War II monument was vandalized.
After two days, the same officer called again and asked him to "come to the office to sign a few papers."
He suspected that he might be asked to sign a statement promising not to leave the city, a sign of potential criminal charges.
At that point, Valentin said, he realized that he did not want "to be kept as a hostage in Russia."
Three hours later, he was on his way to the airport, leaving behind his mother, his studies, and his native country.
"After the second call...I quickly gathered my money and my things, said, 'Bye, Mom,' and left," Valentin said.
A day after arriving in Kiev, he showed up at the Azov Battalion's "training base," he said.
Valentin vocally defended the Azov Battalion, whose reputation for prowess in battle has been clouded by the far-right, even neo-Nazi, views of many members.
The symbol it has used bears a resemblance to the Wolfsangel that was used in Nazi Germany and has been associated with neo-Nazi groups around the world.
On June 10, the U.S. House of Representatives approved amendments to a military spending bill that one of the amendments' backers, Democratic Congressman John Conyers, said was meant to ensure the U.S. military "does not train members of the repulsive neo-Nazi Azov Battalion."
Like many volunteer brigades that were formed in 2014 to fight the rebels, Azov is now part of the National Guard and is under the aegis of the Interior Ministry -- a change that reflects concerns about control over the units.
Asked about descriptions of the Azov Battalion as neo-Nazi or ultranationalist, Valentin said they sound "ridiculous."
"I am a Siberian man with Russian and Belarusian roots," he told RFE/RL.
"There are representatives of various ethnic groups in our battalion: Georgians, Belarusians, Russians, and others. Those who label us as neo-Nazis or Ukrainian ultranationalists just help Russia's propaganda against Ukraine."
Valentin has put his dream of becoming a history teacher on hold -- a decision that dovetails with his concerns about the prevalence of propaganda in the Russian educational system.
"In Russia, education -- especially history teaching -- is too closely tied to the state ideology," he said.
"It tries to teach the young generation that Russia has always been right."
Valentin asked RFE/RL not to publish his surname, saying he fears that the Federal Security Service (FSB) might put pressure on his family and friends back home.
He does not rule out returning to Russia someday, he said -- but "not under the current regime," and not before "everything is in order in Ukraine."
Valentin said he would return if "the tsar falls" or a "revolution starts in Russia."
But he does not place all the blame for what is happening in Russia and Ukraine on Putin.
"We all know very well that the problem is not Putin. We have ourselves to blame for allowing his regime to get established and strengthen," he said.
Source: Radio Free Europe