Re: "pay its fair share of tax" - @ the goalpost-moving politicians:
"...I've not seen anyone argue it's moral or fair."
OK, I'll bite. The loopholes exist because at some point Parliament decided that the system would be *fairer* if an exemption was permitted in specific cases. We call those loopholes. Creating them required more effort than just having a flat rate. They would not exist if MPs didn't think they were fair.