We should pay to keep our ex-leaders safe, no matter what they've done or not done in office, as a matter of principle.
Agreed, to an extent, I am no fan (at all) of Thatcher but accept that if she chose (and was able, I know she is a very ill old lady) to go to Glyncorrwg for example, where she would most definitely not be welcome, on a public visit the security bill would come from the public purse. But should we pay a disproportionate amount (becouse many millions around the world hold them personally responsible for war crimes) for them to jet around the world earning themselves a personal fortune of many millions as Blair does. Especially as he could probably afford to contribute toward it.
(I don't know that he doesn't contribute, haven't been able to find out and I don't think a google search of "Tony Blairs security arrangements" would do much good anyway)