I don't think you are being unreasonable by wanting to become a councillor, in time potentially an MP, starting with volunteering to get some relevant experience in the sector to help. SAHM absolutely can have a lot to offer. And it is absolutely not appropriate or the right thing for the current incumbents to be of the same demographic, men of a similar age. That doesn't help with diversity of thought and understanding different situations. Being a Councillor and trying to give back and improve your local community is a great thing to do.
I don't agree with a lot of your political views, but that's not the point. I am seeing contradictions between your potential career intentions and your viewpoints.
Being a Councillor or MP is a big job. Not a part time gig. You could do it, but would need childcare. You said you are 30, and you worked for 5 years before having kids, so assuming your children are still young. But you don't think it is in their best interests to be in full time childcare and not with a SAHP?
But hand on heart, can you honestly say that toddlers and children are better in full time childcare so that both parents can work? Or teens in the house alone/doing whatever they want a lot as both parents are working?
How are you hoping to achieve this when in a high pressure, long hour position? You wouldn't be at home for your teens as you have stated above you believe is better for them.
I work, currently 4 days, soon to go up to 5, with 2 kids. I absolutely believe that working, if the parent wants to or has to for their families and own financial security is a perfectly acceptable option. My kids have had great times in childcare, making friends, learning in a purpose built environment. And having fun at home too. It is better for me and my mental health to work, and I have flexibility as am self employed. I personally wouldn't want to be a SAHP full time, although I am sometimes envious of those who are fulfilled by parenting full time as they are happy and have less to juggle than a business, household and kids (I know its still stressful and very busy).
However you don't have the same views as me, but are considering a career that would mean you have to live against your values? Is that really what you want?