As an example, I attended a Grammar School in Kent. It attracted people from right across the spectrum in a very mixed income area. Equality of opportunity for me means giving all those who have the capability to attend a high achieving establishment that chance. Greater provision for Grammar schools and ensuring all those eligible would have a place across the board would surely assist in increasing social mobility not reducing it.
I think this is an excellent illustration of why many/most people vote Conservative: the 'common sense' analysis is generally a 'conservative' one, is very appealing and rather straightforward to get across in a brief, clear, simple statement of policy or position.
But it's usually wrong, as in this case. There are lots of studies on the effect of selection and grammar schools, whether in their heyday or recently, and they're rather consistent in finding that a small benefit for those pupils who get into a grammar school (which is predominantly better off kids anyway; relatively few poorer kids get in, because their academic disadvantage is well under way by then) is outweighed by the negatives for those who don't. Studies have demonstrated that in areas with selective schools, income inequalities are
greater than in areas without. You don't get
better schools without also getting
worse schools.
Politics and the multi-dimensional impact of policies across complex social groups is complicated stuff. Common sense answers are appealing, but almost always a gross simplification which makes the problem worse, not better - and in the minds of those who formulate them, if not those who fall for them, deliberately so.
The other particularly prominent reason for voting Tory I think is a disillusionment with the impact governments can have in general. If you feel that they're all as bad as each other, or the system is rigged and that no government can significantly change things, then it's actually reasonably logical to vote for the party that will leave you to your own devices to a greater extent - if you have the means to look after yourself. The party that is generally believed to keep taxes lower and provide the basis for a more stable economy then provides the greater ability to 'look after yourself'. The growing cynicism about politics in general benefits thus also benefits the Tories.