Q:

If the company reduces Roles & Resposibilities , is it professionally acceptable to move to a competitor?

Current startup wants me to dig myself a smaller role, more technical and with progressively fewer responsibilities.
Competitors would hire me for a more senior role, and would be very happy to have access to my business contacts.
Question: if the company is de facto blocking my career development, is it OK to move up at a competitor?

A:

Unless you have a contract forbidding you moving to a competitor, it's always ok to do what is best for your career.
One thing you should not do, however, is to take your current company's business contacts to the competitor.  That is very uncool, at the least, and could open you up to a justified lawsuit.  If the new company only wants you in order to get access to those contacts, be very careful about going there.  If you don't bring them with you (and you should not), they may not want to keep you after all.  So go to the job because they want YOU, not who you know; because you want the job and consider it better than the job you have now.

A:

It is always OK to Move On.
ALWAYS.
You can do it for ANY reason, or for no reason at all.
In the aerospace industry, it used to be absolutely routine for engineers to move from Boeing to Mac Dack to Lockheed to General Dynamics to Mac Dack to Boeing to Northrup to ... every some number of years.  It worked out well for everyone: the guy came back around with a broader perspective, having seen how the Other Guys did things, and learning what worked and what didn't.

