'Because what may be known of God is manifest in them, for God has shown it to them............Who, knowing the righteous judgement of God that those who practise such things are worthy of death......... for when the Gentiles, who do not have the law, by nature do the things of the law, these, although not having the law, are a law to themselves, who show the work of the law written on their hearts, their conscience also bearing witness, and between themselves their thoughts accusing or else excusing them' (Romans 1:19, 32; 2:14-15).
To put it 'gently', you've ripped Ro 2:14-15 out of context. This is no 'universal moral code' that Paul's writing about, it's THE LAW:
6 who will render to every man according to his
works:
7 to them that by
patience in well-doing seek for glory and honor and incorruption, eternal life:
8 but unto them that are factious, and obey not the truth, but obey unrighteousness, shall be wrath and indignation,
9 tribulation and anguish, upon every soul of man that
worketh evil, of the Jew first, and also of the Greek;
10 but glory and honor and peace to every man that
worketh good, to the Jew first, and also to the Greek:
11 for there is no respect of persons with God.
12 For as many as have sinned without law shall also perish without
the law: and as many as have sinned under
the law shall be judged by
the law;
13 for not the hearers of
the law are just before God, but the doers of
the law shall be justified:
14 (for when Gentiles that have not
the law do by nature the things of
the law, these, not having
the law, are
the law unto themselves;
15 in that they show the work of
the law written in their hearts, their conscience bearing witness therewith, and their thoughts one with another accusing or else excusing them);
16 in the day when God shall judge the secrets of men, according to my gospel, by Jesus Christ.
17 But if thou bearest the name of a Jew, and restest upon
the law, and gloriest in God,
18 and knowest his will, and approvest the things that are excellent, being instructed out of
the law,
19 and art confident that thou thyself art a guide of the blind, a light of them that are in darkness,
20 a corrector of the foolish, a teacher of babes, having in
the law the form of knowledge and of the truth;
21 thou therefore that teachest another, teachest thou not thyself? thou that preachest a man should not steal, dost thou steal?
22 thou that sayest a man should not commit adultery, dost thou commit adultery? thou that abhorrest idols, dost thou rob temples?
23 thou who gloriest in
the law, through thy transgression of
the law dishonorest thou God?
24 For the name of God is blasphemed among the Gentiles because of you, even as it is written.
25 For circumcision indeed profiteth, if thou be a doer of
the law: but if thou be a transgressor of
the law, thy circumcision is become uncircumcision.
26 If therefore the uncircumcision keep the ordinances of
the law, shall not his uncircumcision be reckoned for circumcision?
27 and shall not the uncircumcision which is by nature, if it fulfil
the law, judge thee, who with the letter and circumcision art a transgressor of
the law?