Although there are quite a few lists of argumentation fallacies on the web I can't find much about these two:
1)
Julian Baggini describes to argumentation fallacy "If I don’t do it somebody else will" at 

http://www.butterfliesandwheels.org/2002/if-i-dont-do-it-somebody-else-will/

I don't find it anywhere else. Does that fallacy have a special name?

2) Also I can't find the fallacy: "If you don't show me an alternative for my doing you can't criticise it."