Let's take Section 1 PACE 1984 for example, a stop and search for SOAP. Let's say you're on-duty, you come along a lad that you think is acting suspicious. He's an IC3 male and the stop will be in a built up area. You see him walking with a slant, something bulging near the bottom of his ankles all the way up to his knee.
You want to stop and search him, as I said earlier - it's a built up area, loads of people. You stop him, turns out it's nothing but a leg support (the bloke broke his leg a few weeks back).
Think about it, would you risk being known as a 'racist'?