Serious question in that case - why Catholicism?
Because Catholicism contains the fullness of Truth. Others may contain no Truth, some Truth or half of the Truth, only Catholicism contains the fullness of Truth.
Most atheists have no idea about the True role or the
actual Teachings of the Church they form opinions based on a
perceived or incorrect understanding of the Doctrines. Some may think differently if they knew others would still choose to remain ignorant as indeed some Catholics who know but choose repeatedly and publicly in some cases to ignore or deliberately twist the Teachings.
Invincible ignorance caters for those who through no fault of their own were not taught about the Truth of the faith i.e. those who died before Christ, those who died on lands undiscovered by christians throughout history, those who have never heard of Christ or his Church etc. Millions of people.
The real answer to the question “can a non-Catholic enter Heaven?” is
“yes because God makes the ultimate decision on who enters Heaven, not man. And his mercy is infinite Amen”. Mind you if I were a non-Catholic (which I was 5 years ago) I would not be taking that risk, I don’t even consider it to be a “calculated risk” not when we are talking about eternity. I am so lucky I was open enough to listen to our Lady and took the time to research and study church history which brought me home.
Considering we have access to the Church which contains the knowledge and can guide us and light the way to the correct path, there is a higher responsibility placed on Catholics.