His body was not sinful, it did not inherit a sin nature. That is not catholic- that is orthodox.
Indeed... If Christ were born a "slave to sin" like the rest of humanity, He would not have been able to set sinners free. Slaves have no rights. It is only the free men (of which only one existed since the fall, and that one was Jesus Christ) who can work to free slaves.
Hbr 4:15 For we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as [we are, yet] without sin.
Rom 6:1-18 What shall we say then? Shall we continue in sin, that grace may abound? 2 God forbid.
How shall we, that are dead to sin, live any longer therein? 3 Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death? 4 Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life. 5 For if we have been planted together in the likeness of his death, we shall be also [in the likeness] of [his] resurrection: 6
Knowing this, that our old man is crucified with [him], that the body of sin might be destroyed, that the body of sin might be destroyed, that henceforth we should not serve sin. 7 For he that is dead is freed from sin. 8 Now if we be dead with Christ, we believe that we shall also live with him: 9 Knowing that Christ being raised from the dead dieth no more; death hath no more dominion over him. 10 For in that he died, he died unto sin once: but in that he liveth, he liveth unto God. 11
Likewise reckon ye also yourselves to be dead indeed unto sin, but alive unto God through Jesus Christ our Lord. 12 Let not sin therefore reign in your mortal body, that ye should obey it in the lusts thereof. 13 Neither yield ye your members [as] instruments of unrighteousness unto sin: but yield yourselves unto God, as those that are alive from the dead, and your members [as] instruments of righteousness unto God. 14 For sin shall not have dominion over you: for ye are not under the law, but under grace. 15 What then? shall we sin, because we are not under the law, but under grace? God forbid. 16 Know ye not, that to whom ye yield yourselves servants to obey, his servants ye are to whom ye obey; whether of sin unto death, or of obedience unto righteousness? 17 But God be thanked, that
ye were the servants of sin, but ye have obeyed from the heart that form of doctrine which was delivered you. 18
Being then made free from sin, ye became the servants of righteousness.
Paul, writing under the inspiration of the Holy Spirit said that we were slaves to sin -- that the sin nature was in us from the beginning. It was through our "death", indeed the death of Jesus Christ imputed to us, that we are made alive in Christ and no longer slaves to sin.