I did a quick search of 2 Timothy 3 on the Reuniting website here, and did not see citation of 2 Timothy 3, 1-5. You may find the passage supportive of Karezza, or not. Here is the King James Version of the text:
"This know also, that in the last days perilous times shall come.
"2 For men shall be lovers of their own selves, covetous, boasters, proud, blasphemers, disobedient to parents, unthankful, unholy,
"3 Without natural affection, trucebreakers, false accusers, incontinent, fierce, despisers of those that are good,
"4 Traitors, heady, highminded, lovers of pleasures more than lovers of God;
"5 Having a form of godliness, but denying the power thereof: from such turn away..."
The passage lists 'sins' that mark a perilous time in the future. On line 3 is listed 'incontinent.' In my reading of the wonderful, enlightening 'Wisdom' section of this site, I have seen the word 'continent' used to describe the male's ideal state in Karezza intercourse. So, when I see the word 'incontinent' used in any discussion of 'sins', I immediately reread it to see if the writer is hinting at sacred sex, i.e., continent intercourse. I think the writer of 2 Timothy 3 may be stating that continent intercourse is the (known and accepted) preferred method, and that incontinent intercourse is the way of folks engaging in baser actions. (I admit the writer could just be using the word 'incontinent' to mean drunken or other uncontrolled, over-the-top behavior). Just my layman's read!