Well...Membership of the League of the Militant Godless actually exceeded membership of the Communist Party itself...and one could not be a member of the Politburo without being an atheist...so, yea, millions took it very "seriously"...
seriously enough to kill over.
" Between June 1918 and January 1919, official church figures (which did not include the Volga, Kama and several other regions in Russia) claimed that one metropolitan, eighteen bishops, one hundred and two priests, one hundred and fifty-four deacons, and ninety-four monks/nuns had been killed (laity not recorded)
[41]. The estimate of 330 clergy and monastics killed by 1921 may have been an underestimate, due to the fact that 579 monasteries/convents had been liquidated during this period and there were widespread mass executions of monks/nuns during these liquidations"
Treatment of Christians in the Soviet Union - Wikipedia, the free encyclopedia