The problem is that it is a very difficult argument to make - but there is an argument to be made for MPs to be allowed outside interests on the grounds that it attracts a slightly greater breadth of professional people into the House of Commons. MPs also say they are not paid enough. Well that really depends on who you compare them to I suppose. But the difficulty for them is really simple.
It is not like it is the world's biggest secret what MPs are paid. It's right there on the tin when you take the job. More to the point, when all of us send our MPs to the Commons, it is really clear that we want them to represent our interests.
We do not particularly want them to represent the interests of company X or company Y - for any reason. That's the reality. That's why these scandals will keep recurring until, I am afraid, MPs are banned from taking on any outside consultancies, and it doesn't look like that's about to happen.