the use is not a question of ethics or fashion, and the question of the type of tasks that you need to solve
Edwin.Abbo answered on June 10th 19 at 14:23
iframe - a way to insert one HTML page into another page. "Tone" here not and, there are only tasks, such as:
insert form of payment Bank, insert video from YouTube, embedding an advertising banner, etc.
Conrad.Stark answered on June 10th 19 at 14:25
If you mean layout, then it is bad form, if about embedding third-party content, which gives only a js-script, and then embedded via an iframe, then there's nothing wrong with that, other ways not yet invented.