But aren't you just saying that when you have $1 Billion then paying $500k more to a contractor doesn't seem that bad based on the net benefit it would bring to have a dream home.
But imagine if this was a charity (something which govt is, if we look at it a certain way), that inefficiency means more people could have benefited out of it.
India is a case in point, they have enough infrastructure to allow for rapid growth even with a highly corrupt government. While they could do a better job, the increasing standard of living allows for ever improving government services even without increasing efficiency. Further, as standers keep rising the pressure and ability to reduce corruption increases both because governments can directly pay more and because better options show up outside of government.
PS: In the US and I suspect most other countries you can reduce your tax burden by donating just fine. So, taxes are effectively a non issue in terms of charitable donations. Thus tax evasion is simply money people are keeping for personal use.
Consider the cost to build and maintain a road network vs. the benefits it brings.
PS: Further, it's not a question of collecting more money from everyone it's a question of collecting the same money from everyone which is a benefit even if you end up burning the extra money.