The petition site change.org is extremely popular, but many are surprised to learn it is a for-profit corporation. It isn’t a charity, it exists to make money and has investors who expect a return.
Giving a profit-making corporation your real name as well as your opinions on a wide range of topics is not a wise idea in the long term. That sort of data is very valuable to advertisers, and sooner or later a company may be tempted to sell it to them.
For political issues, perhaps the best alternatives are official sites where you can petition governments directly on issues. This more easily gets the attention of people in power, is less likely to sell your data, and governments are often compelled by law to respond to petitions which receive enough signatures. In some countries, popular petitions may trigger a parliamentary debate or even a referendum.
EUROPEAN UNION – European Citizens’ Initiative
GERMANY – Deutscher Bundestag Petitionen
IRELAND – Oireachtas Online Petitions
SCOTLAND – Scottish Parliament Petitions
UNITED KINGDOM – UK Government Petitions