Tight chain... dangerous?

not true....ignore.

Myself and many other track riders (some bigger sprinters than I) use power links so that they can easily swap chains and change gearing at track meetings......power links eliminate stiff links and I've never had a problem with them either on the track or 8 years 5 days a week as a courier.

the most stress a chain will take is a sharp acceleration ( away from traffic lights?) this will be the same whether riding fixed or freewheel, reverse pressure such as skidding or stopping is less anyway.

Yep, this has always been the general consensus through practice...