Wouldn't put all people into one category, regardless of occupation. However police work in any force comes with the shift pattern of earlies, lates and nights, cancelled rest days, difficulties in getting leave, cancelled leave, overtime, finishing shifts late (and probably many other shift work jobs have these issues as well).
On top of that, even the most pure hearted person would undoubtedly be affected by the shift pattern, the things they deal with at work, possibly some ptsd, and generally seeing the underbelly of society all the time. I definitely think the job changes people.
It's a tough job and I'm not discrediting upstanding officers, I couldn't do their job. But the job makes family life and relationships strained at best.
I met my ex before they joined the police, was with them for 10 years and we're now separated. I wouldn't date a police officer again.