Anyone can rise to the level of "live and let live". Anyone can rise to the level of loving one's friends and family. Anyone can come off as a selfless person.
But that is not the purpose of the Catholic Faith.
The purpose of the Catholic Faith is to live out this commandment:
Love one another as I have loved you.
In other words, to rise to the level of loving everyone as God loves.
Anyone who says anything less of the Catholic faith is a liar.
What, after all, is the essence of love? If Christ is right, and the greatest love is to lay down one’s life for one’s friends, then it seems that the essence of all love is this willingness to sacrifice the self for the sake of another: to put the “me” under the heel of your boot and to crush it into a pulp. Even if we aren’t actually being martyred for the sake of our friends, all love has this common factor at its root: self-sacrifice. And if the purpose of our life is to attain to perfect love, then it isn’t good enough to be “nice” or “good” or a “decent chap.” This is pansy stuff. Perfect love means that our entire life, everything that we do, every breath we take, every thought we think, every move we make, is an act of love directed at another: whether our neighbour or God. Perfect love means to be a burning flame of love, to so completely empty ourselves of all self-seeking that the only thing that is left is love – or, in other words, God. This, in fact, is how all the famous mystics talk about the purpose of our life: to literally become a god, by emptying ourselves, and letting God (who is Love) enter in and take the place of the self: to become perfect conduits of God’s love. This is perfection.
Now stop and ask yourself, how do you measure up to this standard? If you’re like me, you don’t even register on the scale. And this is the point: compared to common standards of decency – of the “good chap” – we might be able to muster a passing grade, to convince ourselves that on the whole we’re not doing so bad (certainly we’re doing a heck of a lot better than so-and-so, who you happen to know beats his wife when he gets drunk). But compared to the perfect love which we are called to attain, we are all wretches, without exception. We are all “grievous” sinners.