Are electric shavers kosher? I heard that the son of Rav Moshe Feinstein zal, Rav Reuven Feinstein, said that even though his father permitted them, he would never do so with today’s shavers. Apparently many, many Poskim are against electric Shavers.
Are so many people transgressing a deoraytah? How could some Poskim even forbid scissors, if the Talmud explicitly permits it.
If it’s due to Kabbalistic considerations, how did these chumrot creep into the letter of law.
This is not a question that can be direcly answered. Some write that according to Rav Moshe, today’s shavers are also fine (this is the known opinion of Rav Tendler), and as you point out, many are in practice lenient to use shavers. There is a particular question concerning lift-and-cut technology, and some advise avoiding this. Other poskim are stringent concerning virtually all shavers, but will nonetheless permit using a trimmer that leaves a short stubble.
Poskim don’t generally prohibit scissors al-pi-din, apart from chassidic authorities who absorb much kabbalah material into their ruilngs. The Chafetz Chaim (in nidchei yisrael) is “lenient” concerning this, but I was informed that due to pressure from chassidic groups (especially Chabad), he wrote a special kuntress advising a person not to shave his beard.
For a detailed analysis, see here.