Is your main concern for the safety of the researchers or for the risk of escape of the mutated virus?
I think that virologists are very experienced at containment - small pox was contained for research purposes for a very long time - and so I trust their safety protocols. The disease may well mutate in the wild and we need to be prepared to tackle it so yes, from a lay person's position, I support the ongoing research.
I wonder why they're trying to create mutant variants. Perhaps it's to study how such virulent viruses mutate, with the intention of identifying the strategy that the H5N1 variant is likely to use, and thereby getting an idea of what kind of vaccine could be produced for dealing with possible outbreaks of a deadly variant.
From the little I know about viruses (and bacteria), there's been an on-going battle from time immemorial between microbes and their hosts (our immune systems versus their strategies), but the problem with virulent microbes is that they don't "care" if the host dies, so long as they can spread to the next victim before the current one ceases to provide the environment they need.
If the aim of the research is to get ahead of the game, then I'm in favour of it, but I really hope that containment is the highest priority, and that there is official/governmental oversight of those laboratories.