It might be one thing if with

Grammar: Comparison and Contrast

ならともかく contrasts two situations. The speaker may accept or understand the first, but rejects the second as unreasonable.

A basic translation to English is, “(A) is fine, but (B) is not.”

Usage Notes

The speaker may accept the first situation but judge the second as unreasonable or unacceptable. The pattern often sounds critical.

Formation

ならともかく is formed by attaching it to the plain form of verbs, adjectives, or nouns. Here are the main patterns:
  1. Noun + ならともかく
    • 学生(がくせい)ならともかく社会人(しゃかいじん)はそんな時間(じかん)がない
    • "A student might be one thing, but a working adult doesn't have that kind of time."
  2. Verb (plain form) + ならともかく
    • 勉強(べんきょう)するならともかく(あそ)ぶのは(ゆる)されない
    • "Studying might be one thing, but playing is not allowed."
  3. い-adjective (plain form) + ならともかく
    • (やす)ならともかく(たか)いものは()えない
    • "If it's cheap, that's one thing, but I can't buy expensive things."
  4. な-adjective (stem) + ならともかく
In each case, the phrase introduces the "maybe acceptable" situation, followed by a contrasting statement.

Further Reading

Examples

Indiscriminate murder would be one thing if with 〜ならともかく

Learn the meaning and usage of the grammar 〜ならともかく in Japanese, with examples from manga.
名探偵コナン » Volume 5 » Page 110

Sonoko is invited to a band’s after party. During the get-together, the band’s singer Tatsuya eats a rice ball only to collapse and die. The police are called in, and Inspector Megure discovers the victim was poisoned. He accuses the man who prepared the food, but Conan bites into a rice ball to show it’s safe. The victim’s manager, Mari, agrees.

麻理(まり):
無差別(むさべつ)殺人(さつじん)ならともかく、たまたま達也(たつや)()べたオニギリだけに、あらかじめ(どく)仕込(しこ)むのは不可能(ふかのう)じゃありません?」
“If it were indiscriminate murder, that's one thing but since it was just the rice ball Tatsuya happened to eat, wouldn't it be impossible to poison it beforehand?”
目暮(めぐれ):
「た、(たし)かにそうだが…」
“Th-that's true.”