Contextually speaking, does 1 Corinthians 1:21 in the KJV suggest that preaching is a foolish thing?
For after that in the wisdom of God the world by wisdom knew not God, it pleased God by the foolishness of preaching to save them that believe.
Does the KJV suggest here that it is foolish to preach, or that the act of preaching is foolish?
The KJV does not teach that preaching is foolish. The use of the word "foolish(ness)" here found in its context clears up the confusion.
In verse 18 we read that the "preaching of the cross is to them that perish foolishness." The text isn't saying that it's actually foolishness, but that it is perceived to be this way by certain individuals.
Verse 23 further builds this context by pointing out that the Gospel is "foolishness" to the Greeks, and a stumbling block to the Jews. Again, it's not (in its essense) foolishness (for it's the power of God according to v.18), but instead it's perceived to be foolishness by certain individuals.
Verse 24 tells us further that it is the power of God, and the wisdom of God. And verse 25 states that the foolishness of God is wiser than men, and that the weakness of God is stronger than men. It should be obvious that the author is not actually suggesting his God to have foolishness and weakness, but instead he is making an argument that we ought not look to what man considers wise and strong, since the power of God itself is misidentified by these individuals to be foolishness.
The conclusion is not that preaching is foolish, but that it's perceived to be this way by certain individuals. The NIV states that the message is foolishness, but the same exaplanation stands. The author isn't categorizing the "message of the cross" and "preaching" with foolishness. He's merely using the term loosely.
The word translated "preaching" in verse 18 of the KJV is λόγος which does not refer to the method of delivery but rather the content.
1Co 1:18 For the message about the cross is nonsense to those who are being destroyed, but it is God's power to us who are being saved.
In this context then, λόγος is referring to the "message" which is "inadequately sophisticated" for Greek sophism and rhetorical taste.
BDAG provides a single gloss for μωρία and that is highlighted below:
μωρία, ας, ἡ (μωρός; Soph., Hdt. et al.; PBrem 61, 28 [II A.D.]; PCairMasp 4, 6 Byz.; Sir 20:31; 41:15; Philo; Jos., Ant. 17, 209; Iren. 1, 16, 3 [Harv. I, 162, 2]) foolishness gener. of worldly wisdom (Orig., C. Cels. 7, 47, 9) μ. παρὰ τῷ θεῷ ἐστιν 1 Cor 3:19. Conversely, to all those who are lost 1:18 and esp. to the gentiles vs. 23, the Christian preaching of a Savior who died a slave’s death on the cross was μ. (cp. Theoph. Ant. 2, 1 [p. 94, 7]). It has pleased God to save the believers διὰ τ. μωρίας τοῦ κηρύγματος vs. 21. The ψυχικὸς ἄνθρ. rejects the things of the spirit as μ., 2:14. The Judean temple cult is evaluated as μ. (opp. θεοσέβεια) Dg 3:3.—WCaspari, Über d. bibl. Begriff der Torheit: NKZ 39, 1928, 668–95.—DELG s.v. 1 μωρός. TW. Spicq.
Arndt, W., Danker, F. W., & Bauer, W. (2000). A Greek-English lexicon of the New Testament and other early Christian literature (3rd ed., p. 663). Chicago: University of Chicago Press.
So the word is generally translated "foolishness". However, in the current context Paul's preaching is not said to be "foolishness" but rather that it is viewed that way by people who measure a message by its conformity to popular notions of "scholarship" and "academic style" (such standards recently being an issue on this site).
So the enemies of Paul attack his preaching for its lack of craft and sophistication. In other words, they "down vote" Paul's preaching because it isn't framed in the trappings of Greek scholarship. But Paul defends his preaching saying that the proper measurement of his proclamation is not how styled his preaching is in regards to "sophistication of wording" but rather on effectiveness. Paul says God likes that his message is outside of the comfort zone of the scholars because he has a plan in using such a crude message:
So Paul is saying that the message of God is not insufficiently rhetorically developed but rather it is intentionally deceptively simple so that it can only be valued by those who seek God and is of no appeal to others:
Mat_11:25 At that time Jesus answered and said, I thank thee, O Father, Lord of heaven and earth, because thou hast hid these things from the wise and prudent, and hast revealed them unto babes.
Luk_10:21 In that hour Jesus rejoiced in spirit, and said, I thank thee, O Father, Lord of heaven and earth, that thou hast hid these things from the wise and prudent, and hast revealed them unto babes: even so, Father; for so it seemed good in thy sight.
