It's easy to get caught up in the idea that starting with a negative statement will always set a negative tone, but the truth is, language is nuanced and context matters. Sometimes, starting with a "but first" can actually help to create a more polite and considerate atmosphere, especially when we take the time to acknowledge the other person's perspective or show appreciation for their willingness to listen. Additionally, using "but first" can occasionally make our requests or questions more concise and clear, helping us get straight to the heart of the matter. And while it's important to watch out for negative framing, we shouldn't forget that it's equally possible to use "but first" in a way that highlights the positives and creates a more optimistic tone for our conversations. Ultimately, effective communication comes down to understanding our audience, considering our goals, and choosing our words carefully – whether that involves using "but first" or not.

P.S.: "But" is never a good way to get something across since it by nature discards everything that came before. ;)