Do have some empathy for when job markets or life make people move on. I'd like to stay at an employer for more than 1-2 years, but between the layoffs (avoiding them or getting laid off) or the need for a higher salary that often only comes from switching jobs, its not always possible to build tenure.
Frankly its a big issue in the industry at large. I hate interviewing etc. but I'm not going to get paid 20% less because of it. I had to ride the job hopping treadmill for awhile, and I'd like to get off it just as much as you'd like to see people have more tenure.
When I first started out though, I worked for 5 years at the same place until it was very clear I was going to cap out on being able to advance and merit increases of 3-5% a year aren't going to cut it.