Stallman's position is not extreme. It is consistent and firm, but he tries to reach a reasonable compromise. In political parlance you could say that he's a reformist, not a radical. Notice that he argues that it is OK to use proprietary softare, for example for developing free software if it is the only option, or for communicating with other people that cannot use free software at the moment (e.g., zoom meetings). If that is the case, he urges you to at least tell your colleagues from time to time that there are other options and that you would prefer to use free software:

https://www.gnu.org/philosophy/saying-no-even-once.html

The linked text is very clear and cannot be construed at all as "extreme". At the same time, he holds that while we can reach temporary compromises, proprietary software is always unethical and that we should strive towards freer options.