There are a lot of games that involve moving a ball across a rectangle of ground. One group of players tries to move it to the short end opposite them, while the other group of players tries to move it in the other direction. In the different games there are distinct but relatively inconsequential differences in the number of players, the size and shape of the ball, and the size of the rectangle of ground. The big difference is in how the players move the ball.
If the ball is kicked but never touched by the hands, it's soccer.
If the ball is bounced off the hands but never kicked or carried, it's basketball.
If the ball is kicked and carried, it's football.
If the ball is batted about in nets on sticks, it's lacrosse.
If the ball is scooted around the ground with sticks, it's field hockey.
Any group of people with a convenient ball and ground can decide to play any of those games. It doesn't really matter if they have the "right" number of players, or the "right" ground, or even the "right" ball. The important thing is that once they decide on the game they're playing, everyone moves the ball in the "right" way for that game.
That means that if you're playing soccer you don't pick the ball up and run with it. That move is acceptable in football, but in soccer it's cheating.
It means if you're playing basketball you don't kick the ball. That's acceptable in soccer, but in basketball it's cheating.
Other activities have other sets of rules they must be played by. If you're playing chess, you don't use the rules for dominoes. If you're writing a sonnet, you don't use the rules for writing a haiku. If you're doing traditional Irish step dancing, you don't shimmy your hips. If you're hammering something into two pieces of wood, you don't use a screw. If you're making chocolate fudge, you don't throw in a head of garlic.
And if you're teaching the scientific method, you don't throw in an untestable hypothesis and call it a "theory".
By themselves, there is nothing inherently wrong with any of these actions. But put into the wrong context, they become cheating.
There is nothing inherently wrong with the idea that an "Intelligent Designer" created the universe. Personally I believe it myself. But that idea can never be a scientific theory. An idea becomes a scientific theory by being tested using the scientific method to prove or disprove it. There is no way to scientifically prove or disprove the existence or nonexistence of an "Intelligent Designer", and without that there is no way "Intelligent Design" can ever be a scientific theory.
At this moment there are various attempts being made to inject "Intelligent Design" into science while bypassing the scientific method. Instead, legal and political methods that are used in civil rights cases are being used. There's nothing wrong with using these tactics in civil rights cases. But science isn't a civil rights issue. Science is a different game played by different rules. If you try to inject an idea that hasn't been tested scientifically into science, that's cheating. And if you succeed, the result you get will no longer be science at all. It'll be a whole other ball game.