Poor ol’ Dave needs a crash course on lexical semantics. Let’s give him a few pointers:
1) On the one hand, the same concept can be represented by different words. On the other hand, the same word can represent different concepts.
2) Concepts aren’t necessarily reducible to dictionary definitions. For instance, looking up “Calvinism” in Webster’s is no substitute for the Westminster Confession of Faith.
3) In Biblical usage, “blasphemy” has a secular meaning, viz. slander, calumny, defamation.
4) In Biblical usage, “blasphemy” also as a religious meaning, viz. impiety, sacrilege.
To illustrate the difference, Jesus’ Jewish opponents accuse him of blasphemy (e.g. Mk 2:7; 14:64; Jn 10:33,36). But they don’t do so because he was slandering God. Rather, they do so because he was saying things about himself which are only true of God.
Conversely, John designates the imperial cult as “blasphemous” (Rev 13:1; 17:3). That’s because Caesar demands divine veneration (i.e. veneration proper to God alone).
So the secular sense of “blasphemy” isn’t synonymous with the religious sense of “blasphemy.”
5) We need to distinguish between normative and descriptive usage. Scripture often quotes speakers who don’t represent the editorial viewpoint of the inspired narrator.
Reverting to my earlier example, Jesus’ Jewish opponents accuse him of blasphemy. So that illustrates historical usage. Biblical usage.
But it’s obviously not normative usage. It’s not blasphemous for Christians to affirm the deity of Christ. In fact, it’s impious not to affirm his deity.
Likewise, Stephen is accused of “blasphemy” (Acts 6:11). But that reflects the outlook of his accusers rather than the narrator.
Likewise, Acts 19:37 uses “blasphemy” in a heathen context. But that doesn’t reflect the viewpoint of the Lukan narrator.
6) We need to distinguish between ordinary and technical usage. For instance, the old Catholic Encyclopedia has an entry on “blasphemy,” with a very specialized, Thomistic definition. But it would be anachronistic to read that technical, sectarian definition back into Biblical usage.
7) What’s blasphemous or not depends on your religious outlook. Devout Muslims think it’s sacrilegious to sleep with your feet pointing to Mecca. But that’s not a taboo from a Christian viewpoint.
Likewise, Catholics deem it impious to reject various Marian dogmas. But that’s not sacrilegious from a Protestant perspective.
Gideon desecrates the alter of Baal (Judges 6:28-32). If you’re Jewish, that’s a pious deed–but if you’re a Baal-worshiper, that’s an impious deed.