My family are keen to get a toastmaster at the wedding, so much so they will pay for it. I can't really see the point of one (but then one of the first weddings I will attend will be my own) and I'm worried it will set a "formal" tone to the day when this is something I want to avoid. I am also concerned that the Toastmaster (a stranger) will be too involved in our day. Conversely, my family think it would be unfair/ too much of a responsibility for anyone attending the wedding to take on this role. Am I underestimating the value of a Toastmaster? Perhaps I should be more grateful and learn to pick my battles!
I can understand your concerns but there are toastmasters and toastmasters... Before making your mind up, I think it would help you to meet one to get a feel for what they do and how they do it. The toastmaster will do more than simply introduce the speeches and the toasts, they'll be there to help make sure everything goes to plan and on time. If you don't want an overly formal wedding then choose a toastmaster who will make more casual introductions and perhaps the odd well-placed joke if appropriate. If you don't want them to dress up then ask whether they could come more casually dressed in perhaps a black suit instead of the usual red regalia. They will be working for you so it's up to you to let them know what you would like. There are four professional toast masters we recommend - http://directory.confetti.co.uk/search/keyword/toastmaster/
I don't think you're being ungrateful but if you're still not convinced then it's your call at the end of the day as it's your wedding. My guess is your family are simply trying to help take some of the pressure off. I didn't have a toastmaster at my wedding and looking back, I wish I had done! They can be worth their weight in gold for making sure the day goes as planned.