For the record I think it's totally wrong to punish murder by murdering someone, but putting aside any moral arguments for a minute.
Having the death penalty is a horrible idea that does not make society better for anyone. For one thing, it can be shown that it simply does not work as a deterrent, like, not at all.
Then there's the cost to consider, in many cases, it actually costs more to execute than to imprison people, partly because of the absolutely necessary appeals process to ensure that innocent people are not killed.
Thirdly, even with a rigorous appeals process innocent people will still be murdered by the state.
Now, moving on to the even worse part of your idea, that the death penalty should be used more, for crimes other than murder presumably. This is just a horrible idea.
If you have the death penalty for 'stealing millions of dollars' or 'selling drugs' as well as murder then anyone caught stealing millions of dollars or selling drugs will have absolutely nothing to lose by killing the witnesses.