I agree with the others...every place I've been employed has them, and I've gone between employers over the lasty 30 years without any problems...
How can one employer demand you give up an entire career.
About the only way they might have a chance at enforcing it is if you decided to open a competing shop next door to them or across the street. And even then its going to be expensive for them and not have a guarantee of winning. And the only ones I know of that have actually been enforced, involves someone selling an entire business to someone, then going out and starting up a new one doing the same exact thing (only with a different name) intended to compete directly with the one that was just sold.
Would a Doctor have to give up his career because he left an employer? Would a Solicitor (lawyer) have to do the same if left a firm?
No employer is guaranteeing you a job for life...or would, and yet most non-compete clauses expect you give give up an entire career field. Because every employer in a field actually DOES compete with each other.