Why do I feel grateful for my part time job and flexible working acceptance?

This is what is holding women back, feeling grateful for being paid less! I am happy with my hours but why should I feel 'grateful'? It was advertised as a part time job, there is no requirement, mostly, for me to work extra hours/days. However when a meeting is put in for my day off I feel the need to apologise, sort and pay for additional childcare. Worse is that I think my bosses think I should be grateful and apologetic for not being here full time or when they need me. It is worse for people (mostly women) who have asked to change their full time role to a part time one. In acceptance of these agreements, rather than the employer working to reduce the work load it is the employee who has to 'make it work', often resulting in them doing a full time work load in reduced hours causing more stress. Essentially the employer gets more for their money.

This is just a rant, something I needed to say!

I should also mention that I am a HR Manager and I am sad that I feel powerless in this position to make flexible working a more positive experience.