The slide pins are not the issue. Slide pins will cause uneven wear on the pads...They don't cause brake lock-up. Lock-up is caused by one of two things...Brake fluid pressure isn't coming out of the caliper when the pedal is released (hose, proportioning valve, etc) or the piston square cut seal will not retract the piston(the most likely culprit here). Nothing personal, but I have said it a million times on this forum and the industry preaches it but no one seems to listen...You can't slap pads on at 50K(or whatever) mileage and think you have new brakes, when those pads are being actuated by worn-out calipers. When you push those caliper pistons back in, behind them sits a crud/dirt ring that you push the piston/seal over top of...damaging both and usually starting them down the path to where you are at now.
I'm going to have to respectfully disagree that slide pins won't cause this issue. We also have to agree on what we call 'caliper lock-up.'
Because you're right, if the piston isn't retracting then yes, the caliper is 'locked up.'
However...I find that this RARELY happens. Usually the pins haven't been lubed properly, and they either 'partially freeze' or 'fully-freeze' in position. The piston retracts, so the pad against the piston doesn't wear, but the outer pad remains jammed against the rotor and wears. OR if the pins the outer pad never wears and the inner pad is the only one applying force to the rotor, giving bad wear.
All of these scenarios fall under what the average person (who I always presume I'm dealing with on an internet forum) would call 'frozen' or 'locked up' brakes. Generally the problem is with the pins, NOT the caliper.