"I think people who rationalise tend to be rational. "

I think people who rationalize make up nonsense to justify their BS, which is far from rational.

verb: rationalize; 3rd person present: rationalizes; past tense: rationalized; past participle: rationalized; gerund or present participle: rationalizing; verb: rationalise; 3rd person present: rationalises; past tense: rationalised; past participle: rationalised; gerund or present participle: rationalising

    1.
    attempt to explain or justify (one's own or another's behavior or attitude) with logical, plausible reasons, even if these are not true or appropriate.
    "she couldn't rationalize her urge to return to the cottage"
    synonyms:        justify, explain, explain away, account for, defend, vindicate, excuse More
    "he tried to rationalize his behavior"