Catholics believe that all mankind is made in the image of God. The saints are just the ones who turned out best and we authoritatively know made it to heaven, and thus have achieved the perfection we all had before the Fall. Veneration is not worship, it's more like asking an experienced mentor with access to excellent resources for help.
This all is true as a matter of Church doctrine, but the actual practice among worshippers is rather different (not just in Catholicism - same thing among the Orthodox).
> Catholics believe that all mankind is made in the image of God. The saints are just the ones who turned out best and we authoritatively know made it to heaven
There's a number of problems with that explanation, the three most obvious of which are Ss. Michael, Raphael, and Gabriel.
But the cults of saints aren't limited to those saints that were ever part of mankind, so a theological rationalization of such cults that only applies to human saints doesn't address the issue.
