H.G.
Of course you're not wrong! This is about family, friends, and celebrating your wonderful child! I think the one-year birthday is a big deal, for both baby and mom. My son is only 7 1/2, an we've been to at least 10 one-year birthday parties. It's fun, and who says "no" to a party??
Your in-laws are a pain, like many. (Sorry!) They, of course, are allowed to have their (incredibly irritating) opinions. Do your best to ignore their advice/negativity. They won't stop giving it, in any case. So if possible, try to rise above. And if it's just too much, ask your husband to step up and speak with them privately.
No matter what, enjoy your wonderful kid- and congratulations on a year of fun and craziness!