You're right, the people who vote Reform aren't all idiots. Some of them understand exactly what they're doing, and they are much worse than the idiots.
The people who know what they're doing are deliberately manipulating and exploiting the idiots. The idiots are the ones that are allowing themselves to be manipulated and exploited. They may feel that things are bad right now under Labour, but they don't have any concept of how much worse things could get under Reform. It will be a shock for them if they actually get what they vote for, but it will be too late by the time they realise.
The majority of the electorate will not vote for Reform. None of the polls suggest that this is likely. However, because of our first past the post system, we could end up with a Reform majority in Parliament. This is a quirk of our system, but I think that the majority of voters in the UK remain horrified at the prospect of a Reform government.