I understand the sentiment, but think about it like this: You've been working at a company for six months. Recruiters, good and bad, have been sending you offers to interview for all sorts of jobs. A recruiter finally sends you an opportunity that you can't turn down (2x compensation, more vacation, dream position at dream company, shorter commute with same pay, etc). You interview, you ace it, you get the offer.

Do you turn it down to build more tenure at your current company? Or do you accept because it improves your situation right now?

Rinse, wash, repeat.

Based on the number of emails I've gotten from recruiters (on a stale resume, mind you!), I'd say that "the market" doesn't care about length of time at an employer as much as one might think.