Scrum masters shouldn't be contributing ideas in terms of implementation or design unless they're also part of the dev team. They're there to facilitate. Product owners are probably more akin to "idea guys".
Edit: Even product owner is a bit of a stretch on my part. They're presenting user stories and requirements, which the dev team can pick and choose from the backlog (which, albeit, is prioritized by the product owner).
Edit: Even product owner is a bit of a stretch on my part. They're presenting user stories and requirements, which the dev team can pick and choose from the backlog (which, albeit, is prioritized by the product owner).