" It's that it also makes me feel uncomfortable
It's putting SMT in a new pay scale that we have never been in before.
Part of the discomfort is that my gut says I don't agree."
I'm probably biased here - I'm a former parent governor turned community governor at a primary school - in my area even schools which used to be oversubscribed are having to restructure - there have been government cuts but also the cohorts of children now in primary are smaller than they were.
Your quoted concern these and the issues you raise in the rest of your post last night seem like very reasonable issues.
You're not making the decisions on your own here, but I think you should write down some questions to ask.
Examples - but these may not be relevant to your school, you might know the answers, they might have included these points in the proposal, you might have better and more important questions.
Is the school using current pay scales used across a local authority/academy trust/other wider organisation?
Why do they need to increase pay for management?
What's happening to other staff in the school? Are there non SMT teaching staff who have a good case for higher pay scales or are likely to? Is the school likely to have to make cuts or restructure lower down. Are the staffing needs of the school well covered? How about the state of the building and teaching resources other than staff? Up to date books that meet the needs of the curriculum, for example?
How will doing this or not doing so affect pupils compared to other options? How would news and social media coverage of management giving themselves a big pay rise be seen by other staff, families whose kids attend, the community?
Has there been trade union consultation?
What issues does the school, the area its in, families whose kids attend, the wider organisation, face over the next few years? This goes back to sustainability.
Maybe you'll be persuaded, maybe other governors on the subcommittee will also share concerns, perhaps not.