What does capitalism have to do with RSE?
Welk, for one thing, capitalism is a major driver of the pornification of the society that children of both sexes have to learn to navigate safely. RSE is, broadly speaking, about equipping kids with the knowledge they need to deal with sex out in the world.
Capitalism is part of the context.
It's a fair point that whoever's in power controls what's taught as fact and what's taught as opinion. Which is why schools and teachers are required not to present ideologies and belief systems as The One True Path to Righteousness.
Schools shouldn't be teaching that capitalism must be overthrown, or that it must be maintained. And teachers shouldn't be advocating for the overthrow of existing political and economic systems. It's not their job to indoctrinate children to reject caitalism.
If we had a communist system this rule would require schools not to work with organisations that advocate the overthrow of communism; if we had a proper monarchy the rule would be no teachers advocating for the guillotine.
It's not about left and right, it's about schools being prevented from radicalising children against the Establishment. You teach them how it works, you teach them the pitfalls as well as the benefits, you give them the tools to draw their own conclusions. What you don't do is teach them that the overthrow of the Establishment is imperative.
Personally, I'm okay with that. I find it weird that some people think proponents of all ideologies should be given equal opportunity to indoctrinate kids in schools.