Snicker... Snort... Chortle... GUFFAW!!! ROFL!!!. Danny boy, nothing you have to say regarding the Catholic Church is "plain sense". That you have the effrontery to style your snide, sarcastic, and dishonest question as "plain-sense" reveals much about you, none of it good.
I'll answer, though, for the sake of lurkers. Stripped of its illogical baggage, your question is "How can the Church founded by Jesus of Nazareth, the Christ, the Son of God, have sinners in it?" I suggest you ask Judas Iscariot, he might have an answer for you. You might also ask Simon Peter. He might have some insight into the matter. Jesus promised the He would be with us, His Church, always, and the the gates of Hell would not prevail against His Church. He didn't promise there wouldn't be a few evil people amongst us.
AB
The people who sit in the pews of the Catholic churches are not really the problem here (although they accept the problem), it is the leadership that so often throughout history have preached, no demanded, that their followers behave one way while they are exempt from the same requirements.
I know I will be acused of bigotry, Catholic bashing, etc., just as BibChr has been here, but I've just come to accept that most Catholic defenders on this forum resort to that rather than discuss actual specifics.